webkitgtk-2.16.5HEADwebkitgtk-2.16.5master

1 files changed, 1361 insertions, 959 deletions

diff --git a/Source/WebCore/rendering/RenderBox.cpp b/Source/WebCore/rendering/RenderBox.cpp
index f42232d54..26ce88896 100644
--- a/Source/WebCore/rendering/RenderBox.cpp
+++ b/Source/WebCore/rendering/RenderBox.cpp
@@ -3,7 +3,7 @@
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
- * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
+ * Copyright (C) 2005-2010, 2015 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ -25,43 +25,54 @@
 #include "config.h"
 #include "RenderBox.h"
 
-#include "Chrome.h"
-#include "ChromeClient.h"
+#include "CSSFontSelector.h"
+#include "ControlStates.h"
 #include "Document.h"
 #include "EventHandler.h"
 #include "FloatQuad.h"
+#include "FloatRoundedRect.h"
 #include "Frame.h"
 #include "FrameView.h"
 #include "GraphicsContext.h"
-#include "HTMLElement.h"
+#include "HTMLBodyElement.h"
+#include "HTMLButtonElement.h"
 #include "HTMLFrameOwnerElement.h"
+#include "HTMLHtmlElement.h"
 #include "HTMLInputElement.h"
+#include "HTMLLegendElement.h"
 #include "HTMLNames.h"
+#include "HTMLSelectElement.h"
 #include "HTMLTextAreaElement.h"
 #include "HitTestResult.h"
 #include "InlineElementBox.h"
+#include "MainFrame.h"
 #include "Page.h"
 #include "PaintInfo.h"
 #include "RenderBoxRegionInfo.h"
+#include "RenderChildIterator.h"
+#include "RenderDeprecatedFlexibleBox.h"
 #include "RenderFlexibleBox.h"
-#include "RenderFlowThread.h"
 #include "RenderGeometryMap.h"
 #include "RenderInline.h"
 #include "RenderIterator.h"
 #include "RenderLayer.h"
-#include "RenderRegion.h"
+#include "RenderLayerCompositor.h"
+#include "RenderMultiColumnFlowThread.h"
+#include "RenderNamedFlowFragment.h"
+#include "RenderNamedFlowThread.h"
 #include "RenderTableCell.h"
 #include "RenderTheme.h"
 #include "RenderView.h"
+#include "ScrollAnimator.h"
+#include "ScrollbarTheme.h"
+#include "StyleScrollSnapPoints.h"
 #include "TransformState.h"
 #include "htmlediting.h"
 #include <algorithm>
 #include <math.h>
 #include <wtf/StackStats.h>
 
-#if USE(ACCELERATED_COMPOSITING)
-#include "RenderLayerCompositor.h"
-#endif
+#include "RenderGrid.h"
 
 #if PLATFORM(IOS)
 #include "Settings.h"
@@ -69,56 +80,90 @@
 
 namespace WebCore {
 
+struct SameSizeAsRenderBox : public RenderBoxModelObject {
+    virtual ~SameSizeAsRenderBox() { }
+    LayoutRect frameRect;
+    LayoutBoxExtent marginBox;
+    LayoutUnit preferredLogicalWidths[2];
+    void* pointers[2];
+};
+
+COMPILE_ASSERT(sizeof(RenderBox) == sizeof(SameSizeAsRenderBox), RenderBox_should_stay_small);
+
 using namespace HTMLNames;
 
 // Used by flexible boxes when flexing this element and by table cells.
 typedef WTF::HashMap<const RenderBox*, LayoutUnit> OverrideSizeMap;
-static OverrideSizeMap* gOverrideHeightMap = 0;
-static OverrideSizeMap* gOverrideWidthMap = 0;
+static OverrideSizeMap* gOverrideHeightMap = nullptr;
+static OverrideSizeMap* gOverrideWidthMap = nullptr;
 
 // Used by grid elements to properly size their grid items.
-static OverrideSizeMap* gOverrideContainingBlockLogicalHeightMap = 0;
-static OverrideSizeMap* gOverrideContainingBlockLogicalWidthMap = 0;
-
+typedef WTF::HashMap<const RenderBox*, std::optional<LayoutUnit>> OverrideOptionalSizeMap;
+static OverrideOptionalSizeMap* gOverrideContainingBlockLogicalHeightMap = nullptr;
+static OverrideOptionalSizeMap* gOverrideContainingBlockLogicalWidthMap = nullptr;
+static OverrideSizeMap* gExtraInlineOffsetMap = nullptr;
+static OverrideSizeMap* gExtraBlockOffsetMap = nullptr;
 
 // Size of border belt for autoscroll. When mouse pointer in border belt,
 // autoscroll is started.
 static const int autoscrollBeltSize = 20;
 static const unsigned backgroundObscurationTestMaxDepth = 4;
 
-bool RenderBox::s_hadOverflowClip = false;
+using ControlStatesRendererMap = HashMap<const RenderObject*, std::unique_ptr<ControlStates>>;
+static ControlStatesRendererMap& controlStatesRendererMap()
+{
+    static NeverDestroyed<ControlStatesRendererMap> map;
+    return map;
+}
 
-static bool skipBodyBackground(const RenderBox* bodyElementRenderer)
+static ControlStates* controlStatesForRenderer(const RenderBox& renderer)
 {
-    ASSERT(bodyElementRenderer->isBody());
-    // The <body> only paints its background if the root element has defined a background independent of the body,
-    // or if the <body>'s parent is not the document element's renderer (e.g. inside SVG foreignObject).
-    auto documentElementRenderer = bodyElementRenderer->document().documentElement()->renderer();
-    return documentElementRenderer
-        && !documentElementRenderer->hasBackground()
-        && (documentElementRenderer == bodyElementRenderer->parent());
+    return controlStatesRendererMap().ensure(&renderer, [] {
+        return std::make_unique<ControlStates>();
+    }).iterator->value.get();
 }
 
-RenderBox::RenderBox(Element& element, PassRef<RenderStyle> style, unsigned baseTypeFlags)
-    : RenderBoxModelObject(element, std::move(style), baseTypeFlags)
-    , m_minPreferredLogicalWidth(-1)
-    , m_maxPreferredLogicalWidth(-1)
-    , m_inlineBoxWrapper(0)
+static void removeControlStatesForRenderer(const RenderBox& renderer)
+{
+    controlStatesRendererMap().remove(&renderer);
+}
+
+bool RenderBox::s_hadOverflowClip = false;
+
+RenderBox::RenderBox(Element& element, RenderStyle&& style, BaseTypeFlags baseTypeFlags)
+    : RenderBoxModelObject(element, WTFMove(style), baseTypeFlags)
 {
     setIsBox();
 }
 
-RenderBox::RenderBox(Document& document, PassRef<RenderStyle> style, unsigned baseTypeFlags)
-    : RenderBoxModelObject(document, std::move(style), baseTypeFlags)
-    , m_minPreferredLogicalWidth(-1)
-    , m_maxPreferredLogicalWidth(-1)
-    , m_inlineBoxWrapper(0)
+RenderBox::RenderBox(Document& document, RenderStyle&& style, BaseTypeFlags baseTypeFlags)
+    : RenderBoxModelObject(document, WTFMove(style), baseTypeFlags)
 {
     setIsBox();
 }
 
 RenderBox::~RenderBox()
 {
+    // Do not add any code here. Add it to willBeDestroyed() instead.
+}
+
+void RenderBox::willBeDestroyed()
+{
+    if (frame().eventHandler().autoscrollRenderer() == this)
+        frame().eventHandler().stopAutoscrollTimer(true);
+
+    clearOverrideSize();
+    clearContainingBlockOverrideSize();
+    clearExtraInlineAndBlockOffests();
+
+    RenderBlock::removePercentHeightDescendantIfNeeded(*this);
+
+    ShapeOutsideInfo::removeInfo(*this);
+
+    view().unscheduleLazyRepaint(*this);
+    removeControlStatesForRenderer(*this);
+    
+    RenderBoxModelObject::willBeDestroyed();
 }
 
 RenderRegion* RenderBox::clampToStartAndEndRegions(RenderRegion* region) const
@@ -133,18 +178,28 @@ RenderRegion* RenderBox::clampToStartAndEndRegions(RenderRegion* region) const
     // logical top or logical bottom of the block to size as though the border box in the first and
     // last regions extended infinitely. Otherwise the lines are going to size according to the regions
     // they overflow into, which makes no sense when this block doesn't exist in |region| at all.
-    RenderRegion* startRegion = 0;
-    RenderRegion* endRegion = 0;
-    flowThread->getRegionRangeForBox(this, startRegion, endRegion);
+    RenderRegion* startRegion = nullptr;
+    RenderRegion* endRegion = nullptr;
+    if (!flowThread->getRegionRangeForBox(this, startRegion, endRegion))
+        return region;
 
-    if (startRegion && region->logicalTopForFlowThreadContent() < startRegion->logicalTopForFlowThreadContent())
+    if (region->logicalTopForFlowThreadContent() < startRegion->logicalTopForFlowThreadContent())
         return startRegion;
-    if (endRegion && region->logicalTopForFlowThreadContent() > endRegion->logicalTopForFlowThreadContent())
+    if (region->logicalTopForFlowThreadContent() > endRegion->logicalTopForFlowThreadContent())
         return endRegion;
 
     return region;
 }
 
+bool RenderBox::hasRegionRangeInFlowThread() const
+{
+    RenderFlowThread* flowThread = flowThreadContainingBlock();
+    if (!flowThread || !flowThread->hasValidRegionInfo())
+        return false;
+
+    return flowThread->hasCachedRegionRangeForBox(*this);
+}
+
 LayoutRect RenderBox::clientBoxRectInRegion(RenderRegion* region) const
 {
     if (!region)
@@ -162,17 +217,16 @@ LayoutRect RenderBox::borderBoxRectInRegion(RenderRegion* region, RenderBoxRegio
     if (!region)
         return borderBoxRect();
 
-    RenderFlowThread* flowThread = flowThreadContainingBlock();
-    if (!flowThread)
+    auto* flowThread = flowThreadContainingBlock();
+    if (!is<RenderNamedFlowThread>(flowThread))
         return borderBoxRect();
 
-    RenderRegion* startRegion = 0;
-    RenderRegion* endRegion = 0;
-    flowThread->getRegionRangeForBox(this, startRegion, endRegion);
-    
-    // FIXME: In a perfect world this condition should never happen.
-    if (!startRegion || !endRegion)
+    RenderRegion* startRegion = nullptr;
+    RenderRegion* endRegion = nullptr;
+    if (!flowThread->getRegionRangeForBox(this, startRegion, endRegion)) {
+        // FIXME: In a perfect world this condition should never happen.
         return borderBoxRect();
+    }
 
     ASSERT(flowThread->regionInRange(region, startRegion, endRegion));
 
@@ -184,21 +238,28 @@ LayoutRect RenderBox::borderBoxRectInRegion(RenderRegion* region, RenderBoxRegio
     // We have cached insets.
     LayoutUnit logicalWidth = boxInfo->logicalWidth();
     LayoutUnit logicalLeft = boxInfo->logicalLeft();
-        
+
     // Now apply the parent inset since it is cumulative whenever anything in the containing block chain shifts.
     // FIXME: Doesn't work right with perpendicular writing modes.
     const RenderBlock* currentBox = containingBlock();
-    RenderBoxRegionInfo* currentBoxInfo = currentBox->renderBoxRegionInfo(region);
+    RenderBoxRegionInfo* currentBoxInfo = isRenderFlowThread() ? nullptr : currentBox->renderBoxRegionInfo(region);
     while (currentBoxInfo && currentBoxInfo->isShifted()) {
         if (currentBox->style().direction() == LTR)
             logicalLeft += currentBoxInfo->logicalLeft();
         else
             logicalLeft -= (currentBox->logicalWidth() - currentBoxInfo->logicalWidth()) - currentBoxInfo->logicalLeft();
+
+        // Once we reach the fragmentation container we should stop.
+        if (currentBox->isRenderFlowThread())
+            break;
+
         currentBox = currentBox->containingBlock();
+        if (!currentBox)
+            break;
         region = currentBox->clampToStartAndEndRegions(region);
         currentBoxInfo = currentBox->renderBoxRegionInfo(region);
     }
-    
+
     if (cacheFlag == DoNotCacheRenderBoxRegionInfo)
         delete boxInfo;
 
@@ -207,41 +268,14 @@ LayoutRect RenderBox::borderBoxRectInRegion(RenderRegion* region, RenderBoxRegio
     return LayoutRect(0, logicalLeft, width(), logicalWidth);
 }
 
-void RenderBox::clearRenderBoxRegionInfo()
-{
-    if (isRenderFlowThread())
-        return;
-
-    RenderFlowThread* flowThread = flowThreadContainingBlock();
-    if (flowThread)
-        flowThread->removeRenderBoxRegionInfo(this);
-}
-
-void RenderBox::willBeDestroyed()
+static RenderBlockFlow* outermostBlockContainingFloatingObject(RenderBox& box)
 {
-    if (frame().eventHandler().autoscrollRenderer() == this)
-        frame().eventHandler().stopAutoscrollTimer(true);
-
-    clearOverrideSize();
-    clearContainingBlockOverrideSize();
-
-    RenderBlock::removePercentHeightDescendantIfNeeded(*this);
-
-#if ENABLE(CSS_SHAPES)
-    ShapeOutsideInfo::removeInfo(*this);
-#endif
-
-    RenderBoxModelObject::willBeDestroyed();
-}
-
-RenderBlockFlow* RenderBox::outermostBlockContainingFloatingObject()
-{
-    ASSERT(isFloating());
+    ASSERT(box.isFloating());
     RenderBlockFlow* parentBlock = nullptr;
-    for (auto& ancestor : ancestorsOfType<RenderBlockFlow>(*this)) {
+    for (auto& ancestor : ancestorsOfType<RenderBlockFlow>(box)) {
         if (ancestor.isRenderView())
             break;
-        if (!parentBlock || ancestor.containsFloat(*this))
+        if (!parentBlock || ancestor.containsFloat(box))
             parentBlock = &ancestor;
     }
     return parentBlock;
@@ -251,11 +285,11 @@ void RenderBox::removeFloatingOrPositionedChildFromBlockLists()
 {
     ASSERT(isFloatingOrOutOfFlowPositioned());
 
-    if (documentBeingDestroyed())
+    if (renderTreeBeingDestroyed())
         return;
 
     if (isFloating()) {
-        if (RenderBlockFlow* parentBlock = outermostBlockContainingFloatingObject()) {
+        if (RenderBlockFlow* parentBlock = outermostBlockContainingFloatingObject(*this)) {
             parentBlock->markSiblingsWithFloatsForLayout(this);
             parentBlock->markAllDescendantsWithFloatsForLayout(this, false);
         }
@@ -273,12 +307,10 @@ void RenderBox::styleWillChange(StyleDifference diff, const RenderStyle& newStyl
     if (oldStyle) {
         // The background of the root element or the body element could propagate up to
         // the canvas. Issue full repaint, when our style changes substantially.
-        if (diff >= StyleDifferenceRepaint && (isRoot() || isBody())) {
+        if (diff >= StyleDifferenceRepaint && (isDocumentElementRenderer() || isBody())) {
             view().repaintRootContents();
-#if USE(ACCELERATED_COMPOSITING)
             if (oldStyle->hasEntirelyFixedBackground() != newStyle.hasEntirelyFixedBackground())
                 view().compositor().rootFixedBackgroundsChanged();
-#endif
         }
         
         // When a layout hint happens and an object's position style changes, we have to do a layout
@@ -295,6 +327,16 @@ void RenderBox::styleWillChange(StyleDifference diff, const RenderStyle& newStyl
     } else if (isBody())
         view().repaintRootContents();
 
+#if ENABLE(CSS_SCROLL_SNAP)
+    bool boxContributesSnapPositions = newStyle.scrollSnapArea().hasSnapPosition();
+    if (boxContributesSnapPositions || (oldStyle && oldStyle->scrollSnapArea().hasSnapPosition())) {
+        if (boxContributesSnapPositions)
+            view().registerBoxWithScrollSnapPositions(*this);
+        else
+            view().unregisterBoxWithScrollSnapPositions(*this);
+    }
+#endif
+
     RenderBoxModelObject::styleWillChange(diff, newStyle);
 }
 
@@ -325,12 +367,12 @@ void RenderBox::styleDidChange(StyleDifference diff, const RenderStyle* oldStyle
 
     // If our zoom factor changes and we have a defined scrollLeft/Top, we need to adjust that value into the
     // new zoomed coordinate space.
-    if (hasOverflowClip() && oldStyle && oldStyle->effectiveZoom() != newStyle.effectiveZoom()) {
-        if (int left = layer()->scrollXOffset()) {
+    if (hasOverflowClip() && layer() && oldStyle && oldStyle->effectiveZoom() != newStyle.effectiveZoom()) {
+        if (int left = layer()->scrollOffset().x()) {
             left = (left / oldStyle->effectiveZoom()) * newStyle.effectiveZoom();
             layer()->scrollToXOffset(left);
         }
-        if (int top = layer()->scrollYOffset()) {
+        if (int top = layer()->scrollOffset().y()) {
             top = (top / oldStyle->effectiveZoom()) * newStyle.effectiveZoom();
             layer()->scrollToYOffset(top);
         }
@@ -346,31 +388,36 @@ void RenderBox::styleDidChange(StyleDifference diff, const RenderStyle* oldStyle
     }
 
     bool isBodyRenderer = isBody();
-    bool isRootRenderer = isRoot();
-
-    // Set the text color if we're the body.
-    if (isBodyRenderer)
-        document().setTextColor(newStyle.visitedDependentColor(CSSPropertyColor));
+    bool isDocElementRenderer = isDocumentElementRenderer();
 
-    if (isRootRenderer || isBodyRenderer) {
+    if (isDocElementRenderer || isBodyRenderer) {
         // Propagate the new writing mode and direction up to the RenderView.
-        RenderStyle& viewStyle = view().style();
-        bool viewChangedWritingMode = false;
-        if (viewStyle.direction() != newStyle.direction() && (isRootRenderer || !document().directionSetOnDocumentElement())) {
+        auto* documentElementRenderer = document().documentElement()->renderer();
+        auto& viewStyle = view().mutableStyle();
+        bool rootStyleChanged = false;
+        bool viewDirectionOrWritingModeChanged = false;
+        auto* rootRenderer = isBodyRenderer ? documentElementRenderer : nullptr;
+        if (viewStyle.direction() != newStyle.direction() && (isDocElementRenderer || !documentElementRenderer->style().hasExplicitlySetDirection())) {
             viewStyle.setDirection(newStyle.direction());
-            if (isBodyRenderer)
-                document().documentElement()->renderer()->style().setDirection(newStyle.direction());
+            viewDirectionOrWritingModeChanged = true;
+            if (isBodyRenderer) {
+                rootRenderer->mutableStyle().setDirection(newStyle.direction());
+                rootStyleChanged = true;
+            }
             setNeedsLayoutAndPrefWidthsRecalc();
+
+            view().frameView().topContentDirectionDidChange();
         }
 
-        if (viewStyle.writingMode() != newStyle.writingMode() && (isRootRenderer || !document().writingModeSetOnDocumentElement())) {
+        if (viewStyle.writingMode() != newStyle.writingMode() && (isDocElementRenderer || !documentElementRenderer->style().hasExplicitlySetWritingMode())) {
             viewStyle.setWritingMode(newStyle.writingMode());
-            viewChangedWritingMode = true;
+            viewDirectionOrWritingModeChanged = true;
             view().setHorizontalWritingMode(newStyle.isHorizontalWritingMode());
             view().markAllDescendantsWithFloatsForLayout();
             if (isBodyRenderer) {
-                document().documentElement()->renderer()->style().setWritingMode(newStyle.writingMode());
-                document().documentElement()->renderer()->setHorizontalWritingMode(newStyle.isHorizontalWritingMode());
+                rootStyleChanged = true;
+                rootRenderer->mutableStyle().setWritingMode(newStyle.writingMode());
+                rootRenderer->setHorizontalWritingMode(newStyle.isHorizontalWritingMode());
             }
             setNeedsLayoutAndPrefWidthsRecalc();
         }
@@ -378,19 +425,71 @@ void RenderBox::styleDidChange(StyleDifference diff, const RenderStyle* oldStyle
         view().frameView().recalculateScrollbarOverlayStyle();
         
         const Pagination& pagination = view().frameView().pagination();
-        if (viewChangedWritingMode && pagination.mode != Pagination::Unpaginated) {
+        if (viewDirectionOrWritingModeChanged && pagination.mode != Pagination::Unpaginated) {
             viewStyle.setColumnStylesFromPaginationMode(pagination.mode);
-            if (view().hasColumns() || view().multiColumnFlowThread())
-                view().updateColumnProgressionFromStyle(&viewStyle);
+            if (view().multiColumnFlowThread())
+                view().updateColumnProgressionFromStyle(viewStyle);
         }
+        
+        if (viewDirectionOrWritingModeChanged && view().multiColumnFlowThread())
+            view().updateStylesForColumnChildren();
+        
+        if (rootStyleChanged && is<RenderBlockFlow>(rootRenderer) && downcast<RenderBlockFlow>(*rootRenderer).multiColumnFlowThread())
+            downcast<RenderBlockFlow>(*rootRenderer).updateStylesForColumnChildren();
+        
+        if (isBodyRenderer && pagination.mode != Pagination::Unpaginated && page().paginationLineGridEnabled()) {
+            // Propagate the body font back up to the RenderView and use it as
+            // the basis of the grid.
+            if (newStyle.fontDescription() != view().style().fontDescription()) {
+                view().mutableStyle().setFontDescription(newStyle.fontDescription());
+                view().mutableStyle().fontCascade().update(&document().fontSelector());
+            }
+        }
+
+        if (diff != StyleDifferenceEqual)
+            view().compositor().rootOrBodyStyleChanged(*this, oldStyle);
     }
 
-#if ENABLE(CSS_SHAPES)
-    updateShapeOutsideInfoAfterStyleChange(style(), oldStyle);
+    if ((oldStyle && oldStyle->shapeOutside()) || style().shapeOutside())
+        updateShapeOutsideInfoAfterStyleChange(style(), oldStyle);
+    updateGridPositionAfterStyleChange(style(), oldStyle);
+}
+
+void RenderBox::willBeRemovedFromTree()
+{
+#if ENABLE(CSS_SCROLL_SNAP)
+    if (hasInitializedStyle() && style().scrollSnapArea().hasSnapPosition())
+        view().unregisterBoxWithScrollSnapPositions(*this);
 #endif
+    
+    RenderBoxModelObject::willBeRemovedFromTree();
+}
+    
+
+void RenderBox::updateGridPositionAfterStyleChange(const RenderStyle& style, const RenderStyle* oldStyle)
+{
+    if (!oldStyle || !is<RenderGrid>(parent()))
+        return;
+
+    if (oldStyle->gridItemColumnStart() == style.gridItemColumnStart()
+        && oldStyle->gridItemColumnEnd() == style.gridItemColumnEnd()
+        && oldStyle->gridItemRowStart() == style.gridItemRowStart()
+        && oldStyle->gridItemRowEnd() == style.gridItemRowEnd()
+        && oldStyle->order() == style.order()
+        && oldStyle->hasOutOfFlowPosition() == style.hasOutOfFlowPosition())
+        return;
+
+    // Positioned items don't participate on the layout of the grid,
+    // so we don't need to mark the grid as dirty if they change positions.
+    if (oldStyle->hasOutOfFlowPosition() && style.hasOutOfFlowPosition())
+        return;
+
+    // It should be possible to not dirty the grid in some cases (like moving an
+    // explicitly placed grid item).
+    // For now, it's more simple to just always recompute the grid.
+    downcast<RenderGrid>(*parent()).dirtyGrid();
 }
 
-#if ENABLE(CSS_SHAPES)
 void RenderBox::updateShapeOutsideInfoAfterStyleChange(const RenderStyle& style, const RenderStyle* oldStyle)
 {
     const ShapeValue* shapeOutside = style.shapeOutside();
@@ -409,53 +508,54 @@ void RenderBox::updateShapeOutsideInfoAfterStyleChange(const RenderStyle& style,
     if (!shapeOutside)
         ShapeOutsideInfo::removeInfo(*this);
     else
-        ShapeOutsideInfo::ensureInfo(*this).dirtyShapeSize();
+        ShapeOutsideInfo::ensureInfo(*this).markShapeAsDirty();
 
     if (shapeOutside || shapeOutside != oldShapeOutside)
         markShapeOutsideDependentsForLayout();
 }
-#endif
 
 void RenderBox::updateFromStyle()
 {
     RenderBoxModelObject::updateFromStyle();
 
     const RenderStyle& styleToUse = style();
-    bool isRootObject = isRoot();
+    bool isDocElementRenderer = isDocumentElementRenderer();
     bool isViewObject = isRenderView();
 
     // The root and the RenderView always paint their backgrounds/borders.
-    if (isRootObject || isViewObject)
-        setHasBoxDecorations(true);
+    if (isDocElementRenderer || isViewObject)
+        setHasVisibleBoxDecorations(true);
 
     setFloating(!isOutOfFlowPositioned() && styleToUse.isFloating());
 
     // We also handle <body> and <html>, whose overflow applies to the viewport.
-    if (styleToUse.overflowX() != OVISIBLE && !isRootObject && isRenderBlock()) {
+    if (styleToUse.overflowX() != OVISIBLE && !isDocElementRenderer && isRenderBlock()) {
         bool boxHasOverflowClip = true;
         if (isBody()) {
             // Overflow on the body can propagate to the viewport under the following conditions.
             // (1) The root element is <html>.
             // (2) We are the primary <body> (can be checked by looking at document.body).
             // (3) The root element has visible overflow.
-            if (document().documentElement()->hasTagName(htmlTag)
+            if (is<HTMLHtmlElement>(*document().documentElement())
                 && document().body() == element()
                 && document().documentElement()->renderer()->style().overflowX() == OVISIBLE) {
                 boxHasOverflowClip = false;
             }
         }
-        
         // Check for overflow clip.
         // It's sufficient to just check one direction, since it's illegal to have visible on only one overflow value.
         if (boxHasOverflowClip) {
-            if (!s_hadOverflowClip)
-                // Erase the overflow
-                repaint();
+            if (!s_hadOverflowClip && hasRenderOverflow()) {
+                // Erase the overflow.
+                // Overflow changes have to result in immediate repaints of the entire layout overflow area because
+                // repaints issued by removal of descendants get clipped using the updated style when they shouldn't.
+                repaintRectangle(visualOverflowRect());
+                repaintRectangle(layoutOverflowRect());
+            }
             setHasOverflowClip();
         }
     }
-
-    setHasTransform(styleToUse.hasTransformRelatedProperty());
+    setHasTransformRelatedProperty(styleToUse.hasTransformRelatedProperty());
     setHasReflection(styleToUse.boxReflect());
 }
 
@@ -473,7 +573,7 @@ void RenderBox::layout()
     LayoutStateMaintainer statePusher(view(), *this, locationOffset(), style().isFlippedBlocksWritingMode());
     while (child) {
         if (child->needsLayout())
-            toRenderElement(child)->layout();
+            downcast<RenderElement>(*child).layout();
         ASSERT(!child->needsLayout());
         child = child->nextSibling();
     }
@@ -494,76 +594,77 @@ LayoutUnit RenderBox::clientHeight() const
     return height() - borderTop() - borderBottom() - horizontalScrollbarHeight();
 }
 
-int RenderBox::pixelSnappedClientWidth() const
-{
-    return snapSizeToPixel(clientWidth(), x() + clientLeft());
-}
-
-int RenderBox::pixelSnappedClientHeight() const
-{
-    return snapSizeToPixel(clientHeight(), y() + clientTop());
-}
-
-int RenderBox::pixelSnappedOffsetWidth() const
-{
-    return snapSizeToPixel(offsetWidth(), x() + clientLeft());
-}
-
-int RenderBox::pixelSnappedOffsetHeight() const
-{
-    return snapSizeToPixel(offsetHeight(), y() + clientTop());
-}
-
 int RenderBox::scrollWidth() const
 {
-    if (hasOverflowClip())
+    if (hasOverflowClip() && layer())
         return layer()->scrollWidth();
     // For objects with visible overflow, this matches IE.
     // FIXME: Need to work right with writing modes.
-    if (style().isLeftToRightDirection())
-        return snapSizeToPixel(std::max(clientWidth(), layoutOverflowRect().maxX() - borderLeft()), x() + clientLeft());
-    return clientWidth() - std::min<LayoutUnit>(0, layoutOverflowRect().x() - borderLeft());
+    if (style().isLeftToRightDirection()) {
+        // FIXME: This should use snappedIntSize() instead with absolute coordinates.
+        return roundToInt(std::max(clientWidth(), layoutOverflowRect().maxX() - borderLeft()));
+    }
+    return roundToInt(clientWidth() - std::min<LayoutUnit>(0, layoutOverflowRect().x() - borderLeft()));
 }
 
 int RenderBox::scrollHeight() const
 {
-    if (hasOverflowClip())
+    if (hasOverflowClip() && layer())
         return layer()->scrollHeight();
     // For objects with visible overflow, this matches IE.
     // FIXME: Need to work right with writing modes.
-    return snapSizeToPixel(std::max(clientHeight(), layoutOverflowRect().maxY() - borderTop()), y() + clientTop());
+    // FIXME: This should use snappedIntSize() instead with absolute coordinates.
+    return roundToInt(std::max(clientHeight(), layoutOverflowRect().maxY() - borderTop()));
 }
 
 int RenderBox::scrollLeft() const
 {
-    return hasOverflowClip() ? layer()->scrollXOffset() : 0;
+    return hasOverflowClip() && layer() ? layer()->scrollPosition().x() : 0;
 }
 
 int RenderBox::scrollTop() const
 {
-    return hasOverflowClip() ? layer()->scrollYOffset() : 0;
+    return hasOverflowClip() && layer() ? layer()->scrollPosition().y() : 0;
+}
+
+static void setupWheelEventTestTrigger(RenderLayer& layer)
+{
+    Page& page = layer.renderer().page();
+    if (!page.expectsWheelEventTriggers())
+        return;
+    layer.scrollAnimator().setWheelEventTestTrigger(page.testTrigger());
 }
 
 void RenderBox::setScrollLeft(int newLeft)
 {
-    if (hasOverflowClip())
-        layer()->scrollToXOffset(newLeft, RenderLayer::ScrollOffsetClamped);
+    if (!hasOverflowClip() || !layer())
+        return;
+    setupWheelEventTestTrigger(*layer());
+    layer()->scrollToXPosition(newLeft, RenderLayer::ScrollOffsetClamped);
 }
 
 void RenderBox::setScrollTop(int newTop)
 {
-    if (hasOverflowClip())
-        layer()->scrollToYOffset(newTop, RenderLayer::ScrollOffsetClamped);
+    if (!hasOverflowClip() || !layer())
+        return;
+    setupWheelEventTestTrigger(*layer());
+    layer()->scrollToYPosition(newTop, RenderLayer::ScrollOffsetClamped);
 }
 
 void RenderBox::absoluteRects(Vector<IntRect>& rects, const LayoutPoint& accumulatedOffset) const
 {
-    rects.append(pixelSnappedIntRect(accumulatedOffset, size()));
+    rects.append(snappedIntRect(accumulatedOffset, size()));
 }
 
 void RenderBox::absoluteQuads(Vector<FloatQuad>& quads, bool* wasFixed) const
 {
-    quads.append(localToAbsoluteQuad(FloatRect(0, 0, width(), height()), 0 /* mode */, wasFixed));
+    FloatRect localRect(0, 0, width(), height());
+
+    RenderFlowThread* flowThread = flowThreadContainingBlock();
+    if (flowThread && flowThread->absoluteQuadsForBox(quads, wasFixed, this, localRect.y(), localRect.maxY()))
+        return;
+
+    quads.append(localToAbsoluteQuad(localRect, UseTransforms, wasFixed));
 }
 
 void RenderBox::updateLayerTransform()
@@ -573,7 +674,7 @@ void RenderBox::updateLayerTransform()
         layer()->updateTransform();
 }
 
-LayoutUnit RenderBox::constrainLogicalWidthInRegionByMinMax(LayoutUnit logicalWidth, LayoutUnit availableWidth, RenderBlock* cb, RenderRegion* region) const
+LayoutUnit RenderBox::constrainLogicalWidthInRegionByMinMax(LayoutUnit logicalWidth, LayoutUnit availableWidth, RenderBlock& cb, RenderRegion* region) const
 {
     const RenderStyle& styleToUse = style();
     if (!styleToUse.logicalMaxWidth().isUndefined())
@@ -581,31 +682,33 @@ LayoutUnit RenderBox::constrainLogicalWidthInRegionByMinMax(LayoutUnit logicalWi
     return std::max(logicalWidth, computeLogicalWidthInRegionUsing(MinSize, styleToUse.logicalMinWidth(), availableWidth, cb, region));
 }
 
-LayoutUnit RenderBox::constrainLogicalHeightByMinMax(LayoutUnit logicalHeight) const
+LayoutUnit RenderBox::constrainLogicalHeightByMinMax(LayoutUnit logicalHeight, std::optional<LayoutUnit> intrinsicContentHeight) const
 {
     const RenderStyle& styleToUse = style();
     if (!styleToUse.logicalMaxHeight().isUndefined()) {
-        LayoutUnit maxH = computeLogicalHeightUsing(styleToUse.logicalMaxHeight());
-        if (maxH != -1)
-            logicalHeight = std::min(logicalHeight, maxH);
+        if (std::optional<LayoutUnit> maxH = computeLogicalHeightUsing(MaxSize, styleToUse.logicalMaxHeight(), intrinsicContentHeight))
+            logicalHeight = std::min(logicalHeight, maxH.value());
     }
-    return std::max(logicalHeight, computeLogicalHeightUsing(styleToUse.logicalMinHeight()));
+    if (std::optional<LayoutUnit> computedLogicalHeight = computeLogicalHeightUsing(MinSize, styleToUse.logicalMinHeight(), intrinsicContentHeight))
+        return std::max(logicalHeight, computedLogicalHeight.value());
+    return logicalHeight;
 }
 
-LayoutUnit RenderBox::constrainContentBoxLogicalHeightByMinMax(LayoutUnit logicalHeight) const
+LayoutUnit RenderBox::constrainContentBoxLogicalHeightByMinMax(LayoutUnit logicalHeight, std::optional<LayoutUnit> intrinsicContentHeight) const
 {
     const RenderStyle& styleToUse = style();
     if (!styleToUse.logicalMaxHeight().isUndefined()) {
-        LayoutUnit maxH = computeContentLogicalHeight(styleToUse.logicalMaxHeight());
-        if (maxH != -1)
-            logicalHeight = std::min(logicalHeight, maxH);
+        if (std::optional<LayoutUnit> maxH = computeContentLogicalHeight(MaxSize, styleToUse.logicalMaxHeight(), intrinsicContentHeight))
+            logicalHeight = std::min(logicalHeight, maxH.value());
     }
-    return std::max(logicalHeight, computeContentLogicalHeight(styleToUse.logicalMinHeight()));
+    if (std::optional<LayoutUnit> computedContentLogicalHeight = computeContentLogicalHeight(MinSize, styleToUse.logicalMinHeight(), intrinsicContentHeight))
+        return std::max(logicalHeight, computedContentLogicalHeight.value());
+    return logicalHeight;
 }
 
 RoundedRect::Radii RenderBox::borderRadii() const
 {
-    RenderStyle& style = this->style();
+    auto& style = this->style();
     LayoutRect bounds = frameRect();
 
     unsigned borderLeft = style.borderLeftWidth();
@@ -615,10 +718,19 @@ RoundedRect::Radii RenderBox::borderRadii() const
     return style.getRoundedBorderFor(bounds).radii();
 }
 
+LayoutRect RenderBox::contentBoxRect() const
+{
+    LayoutUnit x = borderLeft() + paddingLeft();
+    if (shouldPlaceBlockDirectionScrollbarOnLeft())
+        x += verticalScrollbarWidth();
+    LayoutUnit y = borderTop() + paddingTop();
+    return LayoutRect(x, y, contentWidth(), contentHeight());
+}
+
 IntRect RenderBox::absoluteContentBox() const
 {
     // This is wrong with transforms and flipped writing modes.
-    IntRect rect = pixelSnappedIntRect(contentBoxRect());
+    IntRect rect = snappedIntRect(contentBoxRect());
     FloatPoint absPos = localToAbsolute();
     rect.move(absPos.x(), absPos.y());
     return rect;
@@ -642,44 +754,20 @@ LayoutRect RenderBox::outlineBoundsForRepaint(const RenderLayerModelObject* repa
         else
             containerRelativeQuad = localToContainerQuad(FloatRect(box), repaintContainer);
 
-        box = containerRelativeQuad.enclosingBoundingBox();
+        box = LayoutRect(containerRelativeQuad.boundingBox());
     }
     
     // FIXME: layoutDelta needs to be applied in parts before/after transforms and
     // repaint containers. https://bugs.webkit.org/show_bug.cgi?id=23308
     box.move(view().layoutDelta());
 
-    return box;
+    return LayoutRect(snapRectToDevicePixels(box, document().deviceScaleFactor()));
 }
 
-void RenderBox::addFocusRingRects(Vector<IntRect>& rects, const LayoutPoint& additionalOffset, const RenderLayerModelObject*)
+void RenderBox::addFocusRingRects(Vector<LayoutRect>& rects, const LayoutPoint& additionalOffset, const RenderLayerModelObject*)
 {
     if (!size().isEmpty())
-        rects.append(pixelSnappedIntRect(additionalOffset, size()));
-}
-
-LayoutRect RenderBox::reflectionBox() const
-{
-    LayoutRect result;
-    if (!style().boxReflect())
-        return result;
-    LayoutRect box = borderBoxRect();
-    result = box;
-    switch (style().boxReflect()->direction()) {
-        case ReflectionBelow:
-            result.move(0, box.height() + reflectionOffset());
-            break;
-        case ReflectionAbove:
-            result.move(0, -box.height() - reflectionOffset());
-            break;
-        case ReflectionLeft:
-            result.move(-box.width() - reflectionOffset(), 0);
-            break;
-        case ReflectionRight:
-            result.move(box.width() + reflectionOffset(), 0);
-            break;
-    }
-    return result;
+        rects.append(LayoutRect(additionalOffset, size()));
 }
 
 int RenderBox::reflectionOffset() const
@@ -722,13 +810,13 @@ bool RenderBox::fixedElementLaysOutRelativeToFrame(const FrameView& frameView) c
 
 bool RenderBox::includeVerticalScrollbarSize() const
 {
-    return hasOverflowClip() && !layer()->hasOverlayScrollbars()
+    return hasOverflowClip() && layer() && !layer()->hasOverlayScrollbars()
         && (style().overflowY() == OSCROLL || style().overflowY() == OAUTO);
 }
 
 bool RenderBox::includeHorizontalScrollbarSize() const
 {
-    return hasOverflowClip() && !layer()->hasOverlayScrollbars()
+    return hasOverflowClip() && layer() && !layer()->hasOverlayScrollbars()
         && (style().overflowX() == OSCROLL || style().overflowX() == OAUTO);
 }
 
@@ -742,18 +830,18 @@ int RenderBox::horizontalScrollbarHeight() const
     return includeHorizontalScrollbarSize() ? layer()->horizontalScrollbarHeight() : 0;
 }
 
-int RenderBox::instrinsicScrollbarLogicalWidth() const
+int RenderBox::intrinsicScrollbarLogicalWidth() const
 {
     if (!hasOverflowClip())
         return 0;
 
-    if (isHorizontalWritingMode() && style().overflowY() == OSCROLL) {
-        ASSERT(layer()->hasVerticalScrollbar());
+    if (isHorizontalWritingMode() && (style().overflowY() == OSCROLL && !hasVerticalScrollbarWithAutoBehavior())) {
+        ASSERT(layer() && layer()->hasVerticalScrollbar());
         return verticalScrollbarWidth();
     }
 
-    if (!isHorizontalWritingMode() && style().overflowX() == OSCROLL) {
-        ASSERT(layer()->hasHorizontalScrollbar());
+    if (!isHorizontalWritingMode() && (style().overflowX() == OSCROLL && !hasHorizontalScrollbarWithAutoBehavior())) {
+        ASSERT(layer() && layer()->hasHorizontalScrollbar());
         return horizontalScrollbarHeight();
     }
 
@@ -782,9 +870,9 @@ bool RenderBox::scroll(ScrollDirection direction, ScrollGranularity granularity,
         return true;
 
     RenderBlock* nextScrollBlock = containingBlock();
-    if (nextScrollBlock && nextScrollBlock->isRenderNamedFlowThread()) {
+    if (is<RenderNamedFlowThread>(nextScrollBlock)) {
         ASSERT(startBox);
-        nextScrollBlock = toRenderFlowThread(nextScrollBlock)->regionFromAbsolutePointAndBox(wheelEventAbsolutePoint, *startBox);
+        nextScrollBlock = downcast<RenderNamedFlowThread>(*nextScrollBlock).fragmentFromAbsolutePointAndBox(wheelEventAbsolutePoint, *startBox);
     }
 
     if (nextScrollBlock && !nextScrollBlock->isRenderView())
@@ -799,7 +887,7 @@ bool RenderBox::logicalScroll(ScrollLogicalDirection direction, ScrollGranularit
     
     RenderLayer* l = layer();
     if (l) {
-#if PLATFORM(MAC)
+#if PLATFORM(COCOA)
         // On Mac only we reset the inline direction position when doing a document scroll (e.g., hitting Home/End).
         if (granularity == ScrollByDocument)
             scrolled = l->scroll(logicalToPhysical(ScrollInlineDirectionBackward, isHorizontalWritingMode(), style().isFlippedBlocksWritingMode()), ScrollByDocument, multiplier);
@@ -825,9 +913,15 @@ bool RenderBox::logicalScroll(ScrollLogicalDirection direction, ScrollGranularit
 
 bool RenderBox::canBeScrolledAndHasScrollableArea() const
 {
-    return canBeProgramaticallyScrolled() && (scrollHeight() != clientHeight() || scrollWidth() != clientWidth());
+    return canBeProgramaticallyScrolled() && (hasHorizontalOverflow() || hasVerticalOverflow());
 }
-    
+
+bool RenderBox::isScrollableOrRubberbandableBox() const
+{
+    return canBeScrolledAndHasScrollableArea();
+}
+
+// FIXME: This is badly named. overflow:hidden can be programmatically scrolled, yet this returns false in that case.
 bool RenderBox::canBeProgramaticallyScrolled() const
 {
     if (isRenderView())
@@ -836,8 +930,7 @@ bool RenderBox::canBeProgramaticallyScrolled() const
     if (!hasOverflowClip())
         return false;
 
-    bool hasScrollableOverflow = hasScrollableOverflowX() || hasScrollableOverflowY();
-    if (scrollsOverflow() && hasScrollableOverflow)
+    if (hasScrollableOverflowX() || hasScrollableOverflowY())
         return true;
 
     return element() && element()->hasEditableStyle();
@@ -872,7 +965,7 @@ bool RenderBox::canAutoscroll() const
 IntSize RenderBox::calculateAutoscrollDirection(const IntPoint& windowPoint) const
 {
     IntRect box(absoluteBoundingBoxRect());
-    box.move(view().frameView().scrollOffset());
+    box.moveBy(view().frameView().scrollPosition());
     IntRect windowBox = view().frameView().contentsToWindow(box);
 
     IntPoint windowAutoscrollPoint = windowPoint;
@@ -892,14 +985,14 @@ IntSize RenderBox::calculateAutoscrollDirection(const IntPoint& windowPoint) con
 
 RenderBox* RenderBox::findAutoscrollable(RenderObject* renderer)
 {
-    while (renderer && !(renderer->isBox() && toRenderBox(renderer)->canAutoscroll())) {
-        if (renderer->isRenderView() && renderer->document().ownerElement())
+    while (renderer && !(is<RenderBox>(*renderer) && downcast<RenderBox>(*renderer).canAutoscroll())) {
+        if (is<RenderView>(*renderer) && renderer->document().ownerElement())
             renderer = renderer->document().ownerElement()->renderer();
         else
             renderer = renderer->parent();
     }
 
-    return renderer && renderer->isBox() ? toRenderBox(renderer) : 0;
+    return is<RenderBox>(renderer) ? downcast<RenderBox>(renderer) : nullptr;
 }
 
 void RenderBox::panScroll(const IntPoint& source)
@@ -908,16 +1001,30 @@ void RenderBox::panScroll(const IntPoint& source)
         layer()->panScrollFromPoint(source);
 }
 
+bool RenderBox::hasVerticalScrollbarWithAutoBehavior() const
+{
+    bool overflowScrollActsLikeAuto = style().overflowY() == OSCROLL && !style().hasPseudoStyle(SCROLLBAR) && ScrollbarTheme::theme().usesOverlayScrollbars();
+    return hasOverflowClip() && (style().overflowY() == OAUTO || style().overflowY() == OOVERLAY || overflowScrollActsLikeAuto);
+}
+
+bool RenderBox::hasHorizontalScrollbarWithAutoBehavior() const
+{
+    bool overflowScrollActsLikeAuto = style().overflowX() == OSCROLL && !style().hasPseudoStyle(SCROLLBAR) && ScrollbarTheme::theme().usesOverlayScrollbars();
+    return hasOverflowClip() && (style().overflowX() == OAUTO || style().overflowX() == OOVERLAY || overflowScrollActsLikeAuto);
+}
+
 bool RenderBox::needsPreferredWidthsRecalculation() const
 {
-    return style().paddingStart().isPercent() || style().paddingEnd().isPercent();
+    return style().paddingStart().isPercentOrCalculated() || style().paddingEnd().isPercentOrCalculated();
 }
 
-IntSize RenderBox::scrolledContentOffset() const
+ScrollPosition RenderBox::scrollPosition() const
 {
-    ASSERT(hasOverflowClip());
+    if (!hasOverflowClip())
+        return { 0, 0 };
+
     ASSERT(hasLayer());
-    return layer()->scrolledContentOffset();
+    return layer()->scrollPosition();
 }
 
 LayoutSize RenderBox::cachedSizeForOverflowClip() const
@@ -927,10 +1034,10 @@ LayoutSize RenderBox::cachedSizeForOverflowClip() const
     return layer()->size();
 }
 
-void RenderBox::applyCachedClipAndScrollOffsetForRepaint(LayoutRect& paintRect) const
+void RenderBox::applyCachedClipAndScrollPositionForRepaint(LayoutRect& paintRect) const
 {
     flipForWritingMode(paintRect);
-    paintRect.move(-scrolledContentOffset()); // For overflow:auto/scroll/hidden.
+    paintRect.moveBy(-scrollPosition()); // For overflow:auto/scroll/hidden.
 
     // Do not clip scroll layer contents to reduce the number of repaints while scrolling.
     if (usesCompositedScrolling()) {
@@ -976,12 +1083,12 @@ LayoutUnit RenderBox::maxPreferredLogicalWidth() const
     return m_maxPreferredLogicalWidth;
 }
 
-bool RenderBox::hasOverrideHeight() const
+bool RenderBox::hasOverrideLogicalContentHeight() const
 {
     return gOverrideHeightMap && gOverrideHeightMap->contains(this);
 }
 
-bool RenderBox::hasOverrideWidth() const
+bool RenderBox::hasOverrideLogicalContentWidth() const
 {
     return gOverrideWidthMap && gOverrideWidthMap->contains(this);
 }
@@ -1020,23 +1127,23 @@ void RenderBox::clearOverrideSize()
 
 LayoutUnit RenderBox::overrideLogicalContentWidth() const
 {
-    ASSERT(hasOverrideWidth());
+    ASSERT(hasOverrideLogicalContentWidth());
     return gOverrideWidthMap->get(this);
 }
 
 LayoutUnit RenderBox::overrideLogicalContentHeight() const
 {
-    ASSERT(hasOverrideHeight());
+    ASSERT(hasOverrideLogicalContentHeight());
     return gOverrideHeightMap->get(this);
 }
 
-LayoutUnit RenderBox::overrideContainingBlockContentLogicalWidth() const
+std::optional<LayoutUnit> RenderBox::overrideContainingBlockContentLogicalWidth() const
 {
     ASSERT(hasOverrideContainingBlockLogicalWidth());
     return gOverrideContainingBlockLogicalWidthMap->get(this);
 }
 
-LayoutUnit RenderBox::overrideContainingBlockContentLogicalHeight() const
+std::optional<LayoutUnit> RenderBox::overrideContainingBlockContentLogicalHeight() const
 {
     ASSERT(hasOverrideContainingBlockLogicalHeight());
     return gOverrideContainingBlockLogicalHeightMap->get(this);
@@ -1052,17 +1159,17 @@ bool RenderBox::hasOverrideContainingBlockLogicalHeight() const
     return gOverrideContainingBlockLogicalHeightMap && gOverrideContainingBlockLogicalHeightMap->contains(this);
 }
 
-void RenderBox::setOverrideContainingBlockContentLogicalWidth(LayoutUnit logicalWidth)
+void RenderBox::setOverrideContainingBlockContentLogicalWidth(std::optional<LayoutUnit> logicalWidth)
 {
     if (!gOverrideContainingBlockLogicalWidthMap)
-        gOverrideContainingBlockLogicalWidthMap = new OverrideSizeMap;
+        gOverrideContainingBlockLogicalWidthMap = new OverrideOptionalSizeMap;
     gOverrideContainingBlockLogicalWidthMap->set(this, logicalWidth);
 }
 
-void RenderBox::setOverrideContainingBlockContentLogicalHeight(LayoutUnit logicalHeight)
+void RenderBox::setOverrideContainingBlockContentLogicalHeight(std::optional<LayoutUnit> logicalHeight)
 {
     if (!gOverrideContainingBlockLogicalHeightMap)
-        gOverrideContainingBlockLogicalHeightMap = new OverrideSizeMap;
+        gOverrideContainingBlockLogicalHeightMap = new OverrideOptionalSizeMap;
     gOverrideContainingBlockLogicalHeightMap->set(this, logicalHeight);
 }
 
@@ -1079,6 +1186,38 @@ void RenderBox::clearOverrideContainingBlockContentLogicalHeight()
         gOverrideContainingBlockLogicalHeightMap->remove(this);
 }
 
+LayoutUnit RenderBox::extraInlineOffset() const
+{
+    return gExtraInlineOffsetMap ? gExtraInlineOffsetMap->get(this) : LayoutUnit();
+}
+
+LayoutUnit RenderBox::extraBlockOffset() const
+{
+    return gExtraBlockOffsetMap ? gExtraBlockOffsetMap->get(this) : LayoutUnit();
+}
+
+void RenderBox::setExtraInlineOffset(LayoutUnit inlineOffest)
+{
+    if (!gExtraInlineOffsetMap)
+        gExtraInlineOffsetMap = new OverrideSizeMap;
+    gExtraInlineOffsetMap->set(this, inlineOffest);
+}
+
+void RenderBox::setExtraBlockOffset(LayoutUnit blockOffest)
+{
+    if (!gExtraBlockOffsetMap)
+        gExtraBlockOffsetMap = new OverrideSizeMap;
+    gExtraBlockOffsetMap->set(this, blockOffest);
+}
+
+void RenderBox::clearExtraInlineAndBlockOffests()
+{
+    if (gExtraInlineOffsetMap)
+        gExtraInlineOffsetMap->remove(this);
+    if (gExtraBlockOffsetMap)
+        gExtraBlockOffsetMap->remove(this);
+}
+
 LayoutUnit RenderBox::adjustBorderBoxLogicalWidthForBoxSizing(LayoutUnit width) const
 {
     LayoutUnit bordersPlusPadding = borderAndPaddingLogicalWidth();
@@ -1102,11 +1241,14 @@ LayoutUnit RenderBox::adjustContentBoxLogicalWidthForBoxSizing(LayoutUnit width)
     return std::max<LayoutUnit>(0, width);
 }
 
-LayoutUnit RenderBox::adjustContentBoxLogicalHeightForBoxSizing(LayoutUnit height) const
+LayoutUnit RenderBox::adjustContentBoxLogicalHeightForBoxSizing(std::optional<LayoutUnit> height) const
 {
+    if (!height)
+        return 0;
+    LayoutUnit result = height.value();
     if (style().boxSizing() == BORDER_BOX)
-        height -= borderAndPaddingLogicalHeight();
-    return std::max<LayoutUnit>(0, height);
+        result -= borderAndPaddingLogicalHeight();
+    return std::max(LayoutUnit(), result);
 }
 
 // Hit Testing
@@ -1122,9 +1264,16 @@ bool RenderBox::nodeAtPoint(const HitTestRequest& request, HitTestResult& result
         }
     }
 
+    RenderFlowThread* flowThread = flowThreadContainingBlock();
+    RenderRegion* regionToUse = flowThread ? downcast<RenderNamedFlowFragment>(flowThread->currentRegion()) : nullptr;
+
+    // If the box is not contained by this region there's no point in going further.
+    if (regionToUse && !flowThread->objectShouldFragmentInFlowRegion(this, regionToUse))
+        return false;
+
     // Check our bounds next. For this purpose always assume that we can only be hit in the
     // foreground phase (which is true for replaced elements like images).
-    LayoutRect boundsRect = borderBoxRectInRegion(locationInContainer.region());
+    LayoutRect boundsRect = borderBoxRectInRegion(regionToUse);
     boundsRect.moveBy(adjustedLocation);
     if (visibleToHitTesting() && action == HitTestForeground && locationInContainer.intersects(boundsRect)) {
         updateHitTestResult(result, locationInContainer.point() - toLayoutSize(adjustedLocation));
@@ -1139,20 +1288,22 @@ bool RenderBox::nodeAtPoint(const HitTestRequest& request, HitTestResult& result
 
 void RenderBox::paintRootBoxFillLayers(const PaintInfo& paintInfo)
 {
+    ASSERT(isDocumentElementRenderer());
     if (paintInfo.skipRootBackground())
         return;
 
-    auto& rootBackgroundRenderer = rendererForRootBackground();
-    
-    const FillLayer* bgLayer = rootBackgroundRenderer.style().backgroundLayers();
-    Color bgColor = rootBackgroundRenderer.style().visitedDependentColor(CSSPropertyBackgroundColor);
+    auto* rootBackgroundRenderer = view().rendererForRootBackground();
+    if (!rootBackgroundRenderer)
+        return;
 
-    paintFillLayers(paintInfo, bgColor, bgLayer, view().backgroundRect(this), BackgroundBleedNone, CompositeSourceOver, &rootBackgroundRenderer);
+    auto& style = rootBackgroundRenderer->style();
+    auto color = style.visitedDependentColor(CSSPropertyBackgroundColor);
+    paintFillLayers(paintInfo, color, style.backgroundLayers(), view().backgroundRect(), BackgroundBleedNone, CompositeSourceOver, rootBackgroundRenderer);
 }
 
-BackgroundBleedAvoidance RenderBox::determineBackgroundBleedAvoidance(GraphicsContext* context) const
+BackgroundBleedAvoidance RenderBox::determineBackgroundBleedAvoidance(GraphicsContext& context) const
 {
-    if (context->paintingDisabled())
+    if (context.paintingDisabled())
         return BackgroundBleedNone;
 
     const RenderStyle& style = this->style();
@@ -1160,7 +1311,7 @@ BackgroundBleedAvoidance RenderBox::determineBackgroundBleedAvoidance(GraphicsCo
     if (!style.hasBackground() || !style.hasBorder() || !style.hasBorderRadius() || borderImageIsLoadedAndCanBeRendered())
         return BackgroundBleedNone;
 
-    AffineTransform ctm = context->getCTM();
+    AffineTransform ctm = context.getCTM();
     FloatSize contextScaling(static_cast<float>(ctm.xScale()), static_cast<float>(ctm.yScale()));
 
     // Because RoundedRect uses IntRect internally the inset applied by the 
@@ -1190,7 +1341,7 @@ void RenderBox::paintBoxDecorations(PaintInfo& paintInfo, const LayoutPoint& pai
     if (!paintInfo.shouldPaintWithinRoot(*this))
         return;
 
-    LayoutRect paintRect = borderBoxRectInRegion(paintInfo.renderRegion);
+    LayoutRect paintRect = borderBoxRectInRegion(currentRenderNamedFlowFragment());
     paintRect.moveBy(paintOffset);
 
 #if PLATFORM(IOS)
@@ -1201,89 +1352,111 @@ void RenderBox::paintBoxDecorations(PaintInfo& paintInfo, const LayoutPoint& pai
         paintRect = IntRect(paintRect.x(), paintRect.y() + (this->height() - height) / 2, width, height); // Vertically center the checkbox, like on desktop
     }
 #endif
-    BackgroundBleedAvoidance bleedAvoidance = determineBackgroundBleedAvoidance(paintInfo.context);
+    BackgroundBleedAvoidance bleedAvoidance = determineBackgroundBleedAvoidance(paintInfo.context());
 
     // FIXME: Should eventually give the theme control over whether the box shadow should paint, since controls could have
     // custom shadows of their own.
-    if (!boxShadowShouldBeAppliedToBackground(bleedAvoidance))
-        paintBoxShadow(paintInfo, paintRect, &style(), Normal);
+    if (!boxShadowShouldBeAppliedToBackground(paintRect.location(), bleedAvoidance))
+        paintBoxShadow(paintInfo, paintRect, style(), Normal);
 
-    GraphicsContextStateSaver stateSaver(*paintInfo.context, false);
+    GraphicsContextStateSaver stateSaver(paintInfo.context(), false);
     if (bleedAvoidance == BackgroundBleedUseTransparencyLayer) {
         // To avoid the background color bleeding out behind the border, we'll render background and border
         // into a transparency layer, and then clip that in one go (which requires setting up the clip before
         // beginning the layer).
-        RoundedRect border = style().getRoundedBorderFor(paintRect, &view());
         stateSaver.save();
-        paintInfo.context->clipRoundedRect(border);
-        paintInfo.context->beginTransparencyLayer(1);
+        paintInfo.context().clipRoundedRect(style().getRoundedBorderFor(paintRect).pixelSnappedRoundedRectForPainting(document().deviceScaleFactor()));
+        paintInfo.context().beginTransparencyLayer(1);
     }
 
     // If we have a native theme appearance, paint that before painting our background.
     // The theme will tell us whether or not we should also paint the CSS background.
-    IntRect snappedPaintRect(pixelSnappedIntRect(paintRect));
-    bool themePainted = style().hasAppearance() && !theme().paint(this, paintInfo, snappedPaintRect);
-    if (!themePainted) {
+    bool borderOrBackgroundPaintingIsNeeded = true;
+    if (style().hasAppearance()) {
+        ControlStates* controlStates = controlStatesForRenderer(*this);
+        borderOrBackgroundPaintingIsNeeded = theme().paint(*this, *controlStates, paintInfo, paintRect);
+        if (controlStates->needsRepaint())
+            view().scheduleLazyRepaint(*this);
+    }
+
+    if (borderOrBackgroundPaintingIsNeeded) {
         if (bleedAvoidance == BackgroundBleedBackgroundOverBorder)
-            paintBorder(paintInfo, paintRect, &style(), bleedAvoidance);
+            paintBorder(paintInfo, paintRect, style(), bleedAvoidance);
 
         paintBackground(paintInfo, paintRect, bleedAvoidance);
 
         if (style().hasAppearance())
-            theme().paintDecorations(this, paintInfo, snappedPaintRect);
+            theme().paintDecorations(*this, paintInfo, paintRect);
     }
-    paintBoxShadow(paintInfo, paintRect, &style(), Inset);
+    paintBoxShadow(paintInfo, paintRect, style(), Inset);
 
     // The theme will tell us whether or not we should also paint the CSS border.
-    if (bleedAvoidance != BackgroundBleedBackgroundOverBorder && (!style().hasAppearance() || (!themePainted && theme().paintBorderOnly(this, paintInfo, snappedPaintRect))) && style().hasBorder())
-        paintBorder(paintInfo, paintRect, &style(), bleedAvoidance);
+    if (bleedAvoidance != BackgroundBleedBackgroundOverBorder && (!style().hasAppearance() || (borderOrBackgroundPaintingIsNeeded && theme().paintBorderOnly(*this, paintInfo, paintRect))) && style().hasVisibleBorderDecoration())
+        paintBorder(paintInfo, paintRect, style(), bleedAvoidance);
 
     if (bleedAvoidance == BackgroundBleedUseTransparencyLayer)
-        paintInfo.context->endTransparencyLayer();
+        paintInfo.context().endTransparencyLayer();
+}
+
+bool RenderBox::paintsOwnBackground() const
+{
+    if (isBody()) {
+        // The <body> only paints its background if the root element has defined a background independent of the body,
+        // or if the <body>'s parent is not the document element's renderer (e.g. inside SVG foreignObject).
+        auto documentElementRenderer = document().documentElement()->renderer();
+        return !documentElementRenderer
+            || documentElementRenderer->hasBackground()
+            || (documentElementRenderer != parent());
+    }
+    
+    return true;
 }
 
 void RenderBox::paintBackground(const PaintInfo& paintInfo, const LayoutRect& paintRect, BackgroundBleedAvoidance bleedAvoidance)
 {
-    if (isRoot()) {
+    if (isDocumentElementRenderer()) {
         paintRootBoxFillLayers(paintInfo);
         return;
     }
-    if (isBody() && skipBodyBackground(this))
+
+    if (!paintsOwnBackground())
         return;
-    if (backgroundIsKnownToBeObscured() && !boxShadowShouldBeAppliedToBackground(bleedAvoidance))
+
+    if (backgroundIsKnownToBeObscured(paintRect.location()) && !boxShadowShouldBeAppliedToBackground(paintRect.location(), bleedAvoidance))
         return;
+
     paintFillLayers(paintInfo, style().visitedDependentColor(CSSPropertyBackgroundColor), style().backgroundLayers(), paintRect, bleedAvoidance);
 }
 
-bool RenderBox::getBackgroundPaintedExtent(LayoutRect& paintedExtent) const
+bool RenderBox::getBackgroundPaintedExtent(const LayoutPoint& paintOffset, LayoutRect& paintedExtent) const
 {
     ASSERT(hasBackground());
-    LayoutRect backgroundRect = pixelSnappedIntRect(borderBoxRect());
+    LayoutRect backgroundRect = snappedIntRect(borderBoxRect());
 
     Color backgroundColor = style().visitedDependentColor(CSSPropertyBackgroundColor);
-    if (backgroundColor.isValid() && backgroundColor.alpha()) {
+    if (backgroundColor.isVisible()) {
         paintedExtent = backgroundRect;
         return true;
     }
 
-    if (!style().backgroundLayers()->image() || style().backgroundLayers()->next()) {
+    auto& layers = style().backgroundLayers();
+    if (!layers.image() || layers.next()) {
         paintedExtent =  backgroundRect;
         return true;
     }
 
-    BackgroundImageGeometry geometry;
-    calculateBackgroundImageGeometry(0, style().backgroundLayers(), backgroundRect, geometry);
+    auto geometry = calculateBackgroundImageGeometry(nullptr, layers, paintOffset, backgroundRect);
     paintedExtent = geometry.destRect();
     return !geometry.hasNonLocalGeometry();
 }
 
 bool RenderBox::backgroundIsKnownToBeOpaqueInRect(const LayoutRect& localRect) const
 {
-    if (isBody() && skipBodyBackground(this))
+    if (!paintsOwnBackground())
         return false;
 
     Color backgroundColor = style().visitedDependentColor(CSSPropertyBackgroundColor);
-    if (!backgroundColor.isValid() || backgroundColor.hasAlpha())
+    if (!backgroundColor.isOpaque())
         return false;
 
     // If the element has appearance, it might be painted by theme.
@@ -1294,11 +1467,15 @@ bool RenderBox::backgroundIsKnownToBeOpaqueInRect(const LayoutRect& localRect) c
         return false;
     // FIXME: Check the opaqueness of background images.
 
+    if (hasClip() || hasClipPath())
+        return false;
+
     // FIXME: Use rounded rect if border radius is present.
     if (style().hasBorderRadius())
         return false;
+    
     // FIXME: The background color clip is defined by the last layer.
-    if (style().backgroundLayers()->next())
+    if (style().backgroundLayers().next())
         return false;
     LayoutRect backgroundRect;
     switch (style().backgroundClip()) {
@@ -1324,22 +1501,20 @@ static bool isCandidateForOpaquenessTest(const RenderBox& childBox)
         return false;
     if (childStyle.visibility() != VISIBLE)
         return false;
-#if ENABLE(CSS_SHAPES)
     if (childStyle.shapeOutside())
         return false;
-#endif
     if (!childBox.width() || !childBox.height())
         return false;
     if (RenderLayer* childLayer = childBox.layer()) {
-#if USE(ACCELERATED_COMPOSITING)
         if (childLayer->isComposited())
             return false;
-#endif
         // FIXME: Deal with z-index.
         if (!childStyle.hasAutoZIndex())
             return false;
         if (childLayer->hasTransform() || childLayer->isTransparent() || childLayer->hasFilter())
             return false;
+        if (!childBox.scrollPosition().isZero())
+            return false;
     }
     return true;
 }
@@ -1372,39 +1547,39 @@ bool RenderBox::foregroundIsKnownToBeOpaqueInRect(const LayoutRect& localRect, u
     return false;
 }
 
-bool RenderBox::computeBackgroundIsKnownToBeObscured()
+bool RenderBox::computeBackgroundIsKnownToBeObscured(const LayoutPoint& paintOffset)
 {
     // Test to see if the children trivially obscure the background.
     // FIXME: This test can be much more comprehensive.
     if (!hasBackground())
         return false;
     // Table and root background painting is special.
-    if (isTable() || isRoot())
+    if (isTable() || isDocumentElementRenderer())
         return false;
 
     LayoutRect backgroundRect;
-    if (!getBackgroundPaintedExtent(backgroundRect))
+    if (!getBackgroundPaintedExtent(paintOffset, backgroundRect))
         return false;
     return foregroundIsKnownToBeOpaqueInRect(backgroundRect, backgroundObscurationTestMaxDepth);
 }
 
 bool RenderBox::backgroundHasOpaqueTopLayer() const
 {
-    const FillLayer* fillLayer = style().backgroundLayers();
-    if (!fillLayer || fillLayer->clip() != BorderFillBox)
+    auto& fillLayer = style().backgroundLayers();
+    if (fillLayer.clip() != BorderFillBox)
         return false;
 
     // Clipped with local scrolling
-    if (hasOverflowClip() && fillLayer->attachment() == LocalBackgroundAttachment)
+    if (hasOverflowClip() && fillLayer.attachment() == LocalBackgroundAttachment)
         return false;
 
-    if (fillLayer->hasOpaqueImage(this) && fillLayer->hasRepeatXY() && fillLayer->image()->canRender(this, style().effectiveZoom()))
+    if (fillLayer.hasOpaqueImage(*this) && fillLayer.hasRepeatXY() && fillLayer.image()->canRender(this, style().effectiveZoom()))
         return true;
 
-    // If there is only one layer and no image, check whether the background color is opaque
-    if (!fillLayer->next() && !fillLayer->hasImage()) {
+    // If there is only one layer and no image, check whether the background color is opaque.
+    if (!fillLayer.next() && !fillLayer.hasImage()) {
         Color bgColor = style().visitedDependentColor(CSSPropertyBackgroundColor);
-        if (bgColor.isValid() && bgColor.alpha() == 255)
+        if (bgColor.isOpaque())
             return true;
     }
 
@@ -1413,13 +1588,22 @@ bool RenderBox::backgroundHasOpaqueTopLayer() const
 
 void RenderBox::paintMask(PaintInfo& paintInfo, const LayoutPoint& paintOffset)
 {
-    if (!paintInfo.shouldPaintWithinRoot(*this) || style().visibility() != VISIBLE || paintInfo.phase != PaintPhaseMask || paintInfo.context->paintingDisabled())
+    if (!paintInfo.shouldPaintWithinRoot(*this) || style().visibility() != VISIBLE || paintInfo.phase != PaintPhaseMask || paintInfo.context().paintingDisabled())
         return;
 
     LayoutRect paintRect = LayoutRect(paintOffset, size());
     paintMaskImages(paintInfo, paintRect);
 }
 
+void RenderBox::paintClippingMask(PaintInfo& paintInfo, const LayoutPoint& paintOffset)
+{
+    if (!paintInfo.shouldPaintWithinRoot(*this) || style().visibility() != VISIBLE || paintInfo.phase != PaintPhaseClippingMask || paintInfo.context().paintingDisabled())
+        return;
+
+    LayoutRect paintRect = LayoutRect(paintOffset, size());
+    paintInfo.context().fillRect(snappedIntRect(paintRect), Color::black);
+}
+
 void RenderBox::paintMaskImages(const PaintInfo& paintInfo, const LayoutRect& paintRect)
 {
     // Figure out if we need to push a transparency layer to render our mask.
@@ -1432,31 +1616,28 @@ void RenderBox::paintMaskImages(const PaintInfo& paintInfo, const LayoutRect& pa
     
     if (!compositedMask || flattenCompositingLayers) {
         pushTransparencyLayer = true;
-        StyleImage* maskBoxImage = style().maskBoxImage().image();
-        const FillLayer* maskLayers = style().maskLayers();
 
         // Don't render a masked element until all the mask images have loaded, to prevent a flash of unmasked content.
-        if (maskBoxImage)
+        if (auto* maskBoxImage = style().maskBoxImage().image())
             allMaskImagesLoaded &= maskBoxImage->isLoaded();
 
-        if (maskLayers)
-            allMaskImagesLoaded &= maskLayers->imagesAreLoaded();
+        allMaskImagesLoaded &= style().maskLayers().imagesAreLoaded();
 
-        paintInfo.context->setCompositeOperation(CompositeDestinationIn);
-        paintInfo.context->beginTransparencyLayer(1);
+        paintInfo.context().setCompositeOperation(CompositeDestinationIn);
+        paintInfo.context().beginTransparencyLayer(1);
         compositeOp = CompositeSourceOver;
     }
 
     if (allMaskImagesLoaded) {
         paintFillLayers(paintInfo, Color(), style().maskLayers(), paintRect, BackgroundBleedNone, compositeOp);
-        paintNinePieceImage(paintInfo.context, paintRect, &style(), style().maskBoxImage(), compositeOp);
+        paintNinePieceImage(paintInfo.context(), paintRect, style(), style().maskBoxImage(), compositeOp);
     }
     
     if (pushTransparencyLayer)
-        paintInfo.context->endTransparencyLayer();
+        paintInfo.context().endTransparencyLayer();
 }
 
-LayoutRect RenderBox::maskClipRect()
+LayoutRect RenderBox::maskClipRect(const LayoutPoint& paintOffset)
 {
     const NinePieceImage& maskBoxImage = style().maskBoxImage();
     if (maskBoxImage.image()) {
@@ -1469,73 +1650,71 @@ LayoutRect RenderBox::maskClipRect()
     
     LayoutRect result;
     LayoutRect borderBox = borderBoxRect();
-    for (const FillLayer* maskLayer = style().maskLayers(); maskLayer; maskLayer = maskLayer->next()) {
+    for (auto* maskLayer = &style().maskLayers(); maskLayer; maskLayer = maskLayer->next()) {
         if (maskLayer->image()) {
-            BackgroundImageGeometry geometry;
             // Masks should never have fixed attachment, so it's OK for paintContainer to be null.
-            calculateBackgroundImageGeometry(0, maskLayer, borderBox, geometry);
-            result.unite(geometry.destRect());
+            result.unite(calculateBackgroundImageGeometry(nullptr, *maskLayer, paintOffset, borderBox).destRect());
         }
     }
     return result;
 }
 
-void RenderBox::paintFillLayers(const PaintInfo& paintInfo, const Color& c, const FillLayer* fillLayer, const LayoutRect& rect,
+void RenderBox::paintFillLayers(const PaintInfo& paintInfo, const Color& color, const FillLayer& fillLayer, const LayoutRect& rect,
     BackgroundBleedAvoidance bleedAvoidance, CompositeOperator op, RenderElement* backgroundObject)
 {
     Vector<const FillLayer*, 8> layers;
-    const FillLayer* curLayer = fillLayer;
     bool shouldDrawBackgroundInSeparateBuffer = false;
-    while (curLayer) {
-        layers.append(curLayer);
+
+    for (auto* layer = &fillLayer; layer; layer = layer->next()) {
+        layers.append(layer);
+
+        if (layer->blendMode() != BlendModeNormal)
+            shouldDrawBackgroundInSeparateBuffer = true;
+
         // Stop traversal when an opaque layer is encountered.
-        // FIXME : It would be possible for the following occlusion culling test to be more aggressive 
+        // FIXME: It would be possible for the following occlusion culling test to be more aggressive
         // on layers with no repeat by testing whether the image covers the layout rect.
         // Testing that here would imply duplicating a lot of calculations that are currently done in
         // RenderBoxModelObject::paintFillLayerExtended. A more efficient solution might be to move
         // the layer recursion into paintFillLayerExtended, or to compute the layer geometry here
         // and pass it down.
 
-        if (!shouldDrawBackgroundInSeparateBuffer && curLayer->blendMode() != BlendModeNormal)
-            shouldDrawBackgroundInSeparateBuffer = true;
-
         // The clipOccludesNextLayers condition must be evaluated first to avoid short-circuiting.
-        if (curLayer->clipOccludesNextLayers(curLayer == fillLayer) && curLayer->hasOpaqueImage(this) && curLayer->image()->canRender(this, style().effectiveZoom()) && curLayer->hasRepeatXY() && curLayer->blendMode() == BlendModeNormal)
+        if (layer->clipOccludesNextLayers(layer == &fillLayer) && layer->hasOpaqueImage(*this) && layer->image()->canRender(this, style().effectiveZoom()) && layer->hasRepeatXY() && layer->blendMode() == BlendModeNormal)
             break;
-        curLayer = curLayer->next();
     }
 
-    GraphicsContext* context = paintInfo.context;
-    if (!context)
-        shouldDrawBackgroundInSeparateBuffer = false;
-    if (shouldDrawBackgroundInSeparateBuffer)
-        context->beginTransparencyLayer(1);
+    auto& context = paintInfo.context();
+    auto baseBgColorUsage = BaseBackgroundColorUse;
 
-    Vector<const FillLayer*>::const_reverse_iterator topLayer = layers.rend();
-    for (Vector<const FillLayer*>::const_reverse_iterator it = layers.rbegin(); it != topLayer; ++it)
-        paintFillLayer(paintInfo, c, *it, rect, bleedAvoidance, op, backgroundObject);
+    if (shouldDrawBackgroundInSeparateBuffer) {
+        paintFillLayer(paintInfo, color, *layers.last(), rect, bleedAvoidance, op, backgroundObject, BaseBackgroundColorOnly);
+        baseBgColorUsage = BaseBackgroundColorSkip;
+        context.beginTransparencyLayer(1);
+    }
+
+    auto topLayer = layers.rend();
+    for (auto it = layers.rbegin(); it != topLayer; ++it)
+        paintFillLayer(paintInfo, color, **it, rect, bleedAvoidance, op, backgroundObject, baseBgColorUsage);
 
     if (shouldDrawBackgroundInSeparateBuffer)
-        context->endTransparencyLayer();
+        context.endTransparencyLayer();
 }
 
-void RenderBox::paintFillLayer(const PaintInfo& paintInfo, const Color& c, const FillLayer* fillLayer, const LayoutRect& rect,
-    BackgroundBleedAvoidance bleedAvoidance, CompositeOperator op, RenderElement* backgroundObject)
+void RenderBox::paintFillLayer(const PaintInfo& paintInfo, const Color& c, const FillLayer& fillLayer, const LayoutRect& rect,
+    BackgroundBleedAvoidance bleedAvoidance, CompositeOperator op, RenderElement* backgroundObject, BaseBackgroundColorUsage baseBgColorUsage)
 {
-    paintFillLayerExtended(paintInfo, c, fillLayer, rect, bleedAvoidance, 0, LayoutSize(), op, backgroundObject);
+    paintFillLayerExtended(paintInfo, c, fillLayer, rect, bleedAvoidance, nullptr, LayoutSize(), op, backgroundObject, baseBgColorUsage);
 }
 
-#if USE(ACCELERATED_COMPOSITING)
-static bool layersUseImage(WrappedImagePtr image, const FillLayer* layers)
+static bool layersUseImage(WrappedImagePtr image, const FillLayer& layers)
 {
-    for (const FillLayer* curLayer = layers; curLayer; curLayer = curLayer->next()) {
-        if (curLayer->image() && image == curLayer->image()->data())
+    for (auto* layer = &layers; layer; layer = layer->next()) {
+        if (layer->image() && image == layer->image()->data())
             return true;
     }
-
     return false;
 }
-#endif
 
 void RenderBox::imageChanged(WrappedImagePtr image, const IntRect*)
 {
@@ -1548,12 +1727,16 @@ void RenderBox::imageChanged(WrappedImagePtr image, const IntRect*)
         return;
     }
 
+    ShapeValue* shapeOutsideValue = style().shapeOutside();
+    if (!view().frameView().isInRenderTreeLayout() && isFloating() && shapeOutsideValue && shapeOutsideValue->image() && shapeOutsideValue->image()->data() == image) {
+        ShapeOutsideInfo::ensureInfo(*this).markShapeAsDirty();
+        markShapeOutsideDependentsForLayout();
+    }
+
     bool didFullRepaint = repaintLayerRectsForImage(image, style().backgroundLayers(), true);
     if (!didFullRepaint)
         repaintLayerRectsForImage(image, style().maskLayers(), false);
 
-
-#if USE(ACCELERATED_COMPOSITING)
     if (!isComposited())
         return;
 
@@ -1561,37 +1744,35 @@ void RenderBox::imageChanged(WrappedImagePtr image, const IntRect*)
         layer()->contentChanged(MaskImageChanged);
     if (layersUseImage(image, style().backgroundLayers()))
         layer()->contentChanged(BackgroundImageChanged);
-#endif
 }
 
-bool RenderBox::repaintLayerRectsForImage(WrappedImagePtr image, const FillLayer* layers, bool drawingBackground)
+bool RenderBox::repaintLayerRectsForImage(WrappedImagePtr image, const FillLayer& layers, bool drawingBackground)
 {
     LayoutRect rendererRect;
-    RenderBox* layerRenderer = 0;
+    RenderBox* layerRenderer = nullptr;
 
-    for (const FillLayer* curLayer = layers; curLayer; curLayer = curLayer->next()) {
-        if (curLayer->image() && image == curLayer->image()->data() && curLayer->image()->canRender(this, style().effectiveZoom())) {
+    for (auto* layer = &layers; layer; layer = layer->next()) {
+        if (layer->image() && image == layer->image()->data() && layer->image()->canRender(this, style().effectiveZoom())) {
             // Now that we know this image is being used, compute the renderer and the rect if we haven't already.
-            bool drawingRootBackground = drawingBackground && (isRoot() || (isBody() && !document().documentElement()->renderer()->hasBackground()));
+            bool drawingRootBackground = drawingBackground && (isDocumentElementRenderer() || (isBody() && !document().documentElement()->renderer()->hasBackground()));
             if (!layerRenderer) {
                 if (drawingRootBackground) {
                     layerRenderer = &view();
 
-                    LayoutUnit rw = toRenderView(*layerRenderer).frameView().contentsWidth();
-                    LayoutUnit rh = toRenderView(*layerRenderer).frameView().contentsHeight();
+                    LayoutUnit rw = downcast<RenderView>(*layerRenderer).frameView().contentsWidth();
+                    LayoutUnit rh = downcast<RenderView>(*layerRenderer).frameView().contentsHeight();
 
                     rendererRect = LayoutRect(-layerRenderer->marginLeft(),
                         -layerRenderer->marginTop(),
-                        std::max(layerRenderer->width() + layerRenderer->marginWidth() + layerRenderer->borderLeft() + layerRenderer->borderRight(), rw),
-                        std::max(layerRenderer->height() + layerRenderer->marginHeight() + layerRenderer->borderTop() + layerRenderer->borderBottom(), rh));
+                        std::max(layerRenderer->width() + layerRenderer->horizontalMarginExtent() + layerRenderer->borderLeft() + layerRenderer->borderRight(), rw),
+                        std::max(layerRenderer->height() + layerRenderer->verticalMarginExtent() + layerRenderer->borderTop() + layerRenderer->borderBottom(), rh));
                 } else {
                     layerRenderer = this;
                     rendererRect = borderBoxRect();
                 }
             }
-
-            BackgroundImageGeometry geometry;
-            layerRenderer->calculateBackgroundImageGeometry(0, curLayer, rendererRect, geometry);
+            // FIXME: Figure out how to pass absolute position to calculateBackgroundImageGeometry (for pixel snapping)
+            BackgroundImageGeometry geometry = layerRenderer->calculateBackgroundImageGeometry(nullptr, *layer, LayoutPoint(), rendererRect);
             if (geometry.hasNonLocalGeometry()) {
                 // Rather than incur the costs of computing the paintContainer for renderers with fixed backgrounds
                 // in order to get the right destRect, just repaint the entire renderer.
@@ -1599,15 +1780,15 @@ bool RenderBox::repaintLayerRectsForImage(WrappedImagePtr image, const FillLayer
                 return true;
             }
             
-            IntRect rectToRepaint = geometry.destRect();
+            LayoutRect rectToRepaint = geometry.destRect();
             bool shouldClipToLayer = true;
 
             // If this is the root background layer, we may need to extend the repaintRect if the FrameView has an
             // extendedBackground. We should only extend the rect if it is already extending the full width or height
             // of the rendererRect.
-            if (drawingRootBackground && view().frameView().hasExtendedBackground()) {
+            if (drawingRootBackground && view().frameView().hasExtendedBackgroundRectForPainting()) {
                 shouldClipToLayer = false;
-                IntRect extendedBackgroundRect = view().frameView().extendedBackgroundRect();
+                IntRect extendedBackgroundRect = view().frameView().extendedBackgroundRectForPainting();
                 if (rectToRepaint.width() == rendererRect.width()) {
                     rectToRepaint.move(extendedBackgroundRect.x(), 0);
                     rectToRepaint.setWidth(extendedBackgroundRect.width());
@@ -1618,7 +1799,7 @@ bool RenderBox::repaintLayerRectsForImage(WrappedImagePtr image, const FillLayer
                 }
             }
 
-            layerRenderer->repaintRectangle(rectToRepaint, false, shouldClipToLayer);
+            layerRenderer->repaintRectangle(rectToRepaint, shouldClipToLayer);
             if (geometry.destRect() == rendererRect)
                 return true;
         }
@@ -1626,28 +1807,6 @@ bool RenderBox::repaintLayerRectsForImage(WrappedImagePtr image, const FillLayer
     return false;
 }
 
-#if PLATFORM(MAC)
-
-void RenderBox::paintCustomHighlight(const LayoutPoint& paintOffset, const AtomicString& type, bool behindText)
-{
-    Page* page = frame().page();
-    if (!page)
-        return;
-
-    InlineBox* boxWrap = inlineBoxWrapper();
-    RootInlineBox* r = boxWrap ? &boxWrap->root() : 0;
-    if (r) {
-        FloatRect rootRect(paintOffset.x() + r->x(), paintOffset.y() + r->selectionTop(), r->logicalWidth(), r->selectionHeight());
-        FloatRect imageRect(paintOffset.x() + x(), rootRect.y(), width(), rootRect.height());
-        page->chrome().client().paintCustomHighlight(element(), type, imageRect, rootRect, behindText, false);
-    } else {
-        FloatRect imageRect(paintOffset.x() + x(), paintOffset.y() + y(), width(), height());
-        page->chrome().client().paintCustomHighlight(element(), type, imageRect, imageRect, behindText, false);
-    }
-}
-
-#endif
-
 bool RenderBox::pushContentsClip(PaintInfo& paintInfo, const LayoutPoint& accumulatedOffset)
 {
     if (paintInfo.phase == PaintPhaseBlockBackground || paintInfo.phase == PaintPhaseSelfOutline || paintInfo.phase == PaintPhaseMask)
@@ -1666,11 +1825,12 @@ bool RenderBox::pushContentsClip(PaintInfo& paintInfo, const LayoutPoint& accumu
         paintObject(paintInfo, accumulatedOffset);
         paintInfo.phase = PaintPhaseChildBlockBackgrounds;
     }
-    IntRect clipRect = pixelSnappedIntRect(isControlClip ? controlClipRect(accumulatedOffset) : overflowClipRect(accumulatedOffset, paintInfo.renderRegion, IgnoreOverlayScrollbarSize, paintInfo.phase));
-    paintInfo.context->save();
+    float deviceScaleFactor = document().deviceScaleFactor();
+    FloatRect clipRect = snapRectToDevicePixels((isControlClip ? controlClipRect(accumulatedOffset) : overflowClipRect(accumulatedOffset, currentRenderNamedFlowFragment(), IgnoreOverlayScrollbarSize, paintInfo.phase)), deviceScaleFactor);
+    paintInfo.context().save();
     if (style().hasBorderRadius())
-        paintInfo.context->clipRoundedRect(style().getRoundedInnerBorderFor(LayoutRect(accumulatedOffset, size())));
-    paintInfo.context->clip(clipRect);
+        paintInfo.context().clipRoundedRect(style().getRoundedInnerBorderFor(LayoutRect(accumulatedOffset, size())).pixelSnappedRoundedRectForPainting(deviceScaleFactor));
+    paintInfo.context().clip(clipRect);
     return true;
 }
 
@@ -1678,7 +1838,7 @@ void RenderBox::popContentsClip(PaintInfo& paintInfo, PaintPhase originalPhase,
 {
     ASSERT(hasControlClip() || (hasOverflowClip() && !layer()->isSelfPaintingLayer()));
 
-    paintInfo.context->restore();
+    paintInfo.context().restore();
     if (originalPhase == PaintPhaseOutline) {
         paintInfo.phase = PaintPhaseSelfOutline;
         paintObject(paintInfo, accumulatedOffset);
@@ -1696,11 +1856,11 @@ LayoutRect RenderBox::overflowClipRect(const LayoutPoint& location, RenderRegion
     clipRect.setSize(clipRect.size() - LayoutSize(borderLeft() + borderRight(), borderTop() + borderBottom()));
 
     // Subtract out scrollbars if we have them.
-     if (layer()) {
-        if (style().shouldPlaceBlockDirectionScrollbarOnLogicalLeft())
+    if (layer()) {
+        if (shouldPlaceBlockDirectionScrollbarOnLeft())
             clipRect.move(layer()->verticalScrollbarWidth(relevancy), 0);
         clipRect.contract(layer()->verticalScrollbarWidth(relevancy), layer()->horizontalScrollbarHeight(relevancy));
-     }
+    }
 
     return clipRect;
 }
@@ -1734,17 +1894,18 @@ LayoutRect RenderBox::clipRect(const LayoutPoint& location, RenderRegion* region
     return clipRect;
 }
 
-LayoutUnit RenderBox::shrinkLogicalWidthToAvoidFloats(LayoutUnit childMarginStart, LayoutUnit childMarginEnd, const RenderBlock* cb, RenderRegion* region) const
+LayoutUnit RenderBox::shrinkLogicalWidthToAvoidFloats(LayoutUnit childMarginStart, LayoutUnit childMarginEnd, const RenderBlock& cb, RenderRegion* region) const
 {    
-    RenderRegion* containingBlockRegion = 0;
+    RenderRegion* containingBlockRegion = nullptr;
     LayoutUnit logicalTopPosition = logicalTop();
     if (region) {
         LayoutUnit offsetFromLogicalTopOfRegion = region ? region->logicalTopForFlowThreadContent() - offsetFromLogicalTopOfFirstPage() : LayoutUnit();
         logicalTopPosition = std::max(logicalTopPosition, logicalTopPosition + offsetFromLogicalTopOfRegion);
-        containingBlockRegion = cb->clampToStartAndEndRegions(region);
+        containingBlockRegion = cb.clampToStartAndEndRegions(region);
     }
 
-    LayoutUnit result = cb->availableLogicalWidthForLineInRegion(logicalTopPosition, false, containingBlockRegion) - childMarginStart - childMarginEnd;
+    LayoutUnit logicalHeight = cb.logicalHeightForChild(*this);
+    LayoutUnit result = cb.availableLogicalWidthForLineInRegion(logicalTopPosition, DoNotIndentText, containingBlockRegion, logicalHeight) - childMarginStart - childMarginEnd;
 
     // We need to see if margins on either the start side or the end side can contain the floats in question. If they can,
     // then just using the line width is inaccurate. In the case where a float completely fits, we don't need to use the line
@@ -1752,9 +1913,9 @@ LayoutUnit RenderBox::shrinkLogicalWidthToAvoidFloats(LayoutUnit childMarginStar
     // doesn't fit, we can use the line offset, but we need to grow it by the margin to reflect the fact that the margin was
     // "consumed" by the float. Negative margins aren't consumed by the float, and so we ignore them.
     if (childMarginStart > 0) {
-        LayoutUnit startContentSide = cb->startOffsetForContent(containingBlockRegion);
+        LayoutUnit startContentSide = cb.startOffsetForContent(containingBlockRegion);
         LayoutUnit startContentSideWithMargin = startContentSide + childMarginStart;
-        LayoutUnit startOffset = cb->startOffsetForLineInRegion(logicalTopPosition, false, containingBlockRegion);
+        LayoutUnit startOffset = cb.startOffsetForLineInRegion(logicalTopPosition, DoNotIndentText, containingBlockRegion, logicalHeight);
         if (startOffset > startContentSideWithMargin)
             result += childMarginStart;
         else
@@ -1762,9 +1923,9 @@ LayoutUnit RenderBox::shrinkLogicalWidthToAvoidFloats(LayoutUnit childMarginStar
     }
     
     if (childMarginEnd > 0) {
-        LayoutUnit endContentSide = cb->endOffsetForContent(containingBlockRegion);
+        LayoutUnit endContentSide = cb.endOffsetForContent(containingBlockRegion);
         LayoutUnit endContentSideWithMargin = endContentSide + childMarginEnd;
-        LayoutUnit endOffset = cb->endOffsetForLineInRegion(logicalTopPosition, false, containingBlockRegion);
+        LayoutUnit endOffset = cb.endOffsetForLineInRegion(logicalTopPosition, DoNotIndentText, containingBlockRegion, logicalHeight);
         if (endOffset > endContentSideWithMargin)
             result += childMarginEnd;
         else
@@ -1776,24 +1937,26 @@ LayoutUnit RenderBox::shrinkLogicalWidthToAvoidFloats(LayoutUnit childMarginStar
 
 LayoutUnit RenderBox::containingBlockLogicalWidthForContent() const
 {
-    if (hasOverrideContainingBlockLogicalWidth())
-        return overrideContainingBlockContentLogicalWidth();
+    if (hasOverrideContainingBlockLogicalWidth()) {
+        if (auto overrideLogicalWidth = overrideContainingBlockContentLogicalWidth())
+            return overrideLogicalWidth.value();
+    }
 
-    RenderBlock* cb = containingBlock();
-    if (!cb)
-        return LayoutUnit();
-    return cb->availableLogicalWidth();
+    if (RenderBlock* cb = containingBlock())
+        return cb->availableLogicalWidth();
+    return LayoutUnit();
 }
 
 LayoutUnit RenderBox::containingBlockLogicalHeightForContent(AvailableLogicalHeightType heightType) const
 {
-    if (hasOverrideContainingBlockLogicalHeight())
-        return overrideContainingBlockContentLogicalHeight();
+    if (hasOverrideContainingBlockLogicalHeight()) {
+        if (auto overrideLogicalHeight = overrideContainingBlockContentLogicalHeight())
+            return overrideLogicalHeight.value();
+    }
 
-    RenderBlock* cb = containingBlock();
-    if (!cb)
-        return LayoutUnit();
-    return cb->availableLogicalHeight(heightType);
+    if (RenderBlock* cb = containingBlock())
+        return cb->availableLogicalHeight(heightType);
+    return LayoutUnit();
 }
 
 LayoutUnit RenderBox::containingBlockLogicalWidthForContentInRegion(RenderRegion* region) const
@@ -1815,23 +1978,25 @@ LayoutUnit RenderBox::containingBlockLogicalWidthForContentInRegion(RenderRegion
 LayoutUnit RenderBox::containingBlockAvailableLineWidthInRegion(RenderRegion* region) const
 {
     RenderBlock* cb = containingBlock();
-    RenderRegion* containingBlockRegion = 0;
+    RenderRegion* containingBlockRegion = nullptr;
     LayoutUnit logicalTopPosition = logicalTop();
     if (region) {
         LayoutUnit offsetFromLogicalTopOfRegion = region ? region->logicalTopForFlowThreadContent() - offsetFromLogicalTopOfFirstPage() : LayoutUnit();
         logicalTopPosition = std::max(logicalTopPosition, logicalTopPosition + offsetFromLogicalTopOfRegion);
         containingBlockRegion = cb->clampToStartAndEndRegions(region);
     }
-    return cb->availableLogicalWidthForLineInRegion(logicalTopPosition, false, containingBlockRegion, availableLogicalHeight(IncludeMarginBorderPadding));
+    return cb->availableLogicalWidthForLineInRegion(logicalTopPosition, DoNotIndentText, containingBlockRegion, availableLogicalHeight(IncludeMarginBorderPadding));
 }
 
 LayoutUnit RenderBox::perpendicularContainingBlockLogicalHeight() const
 {
-    if (hasOverrideContainingBlockLogicalHeight())
-        return overrideContainingBlockContentLogicalHeight();
+    if (hasOverrideContainingBlockLogicalHeight()) {
+        if (auto overrideLogicalHeight = overrideContainingBlockContentLogicalHeight())
+            return overrideLogicalHeight.value();
+    }
 
     RenderBlock* cb = containingBlock();
-    if (cb->hasOverrideHeight())
+    if (cb->hasOverrideLogicalContentHeight())
         return cb->overrideLogicalContentHeight();
 
     const RenderStyle& containingBlockStyle = cb->style();
@@ -1841,11 +2006,13 @@ LayoutUnit RenderBox::perpendicularContainingBlockLogicalHeight() const
     if (!logicalHeightLength.isFixed()) {
         LayoutUnit fillFallbackExtent = containingBlockStyle.isHorizontalWritingMode() ? view().frameView().visibleHeight() : view().frameView().visibleWidth();
         LayoutUnit fillAvailableExtent = containingBlock()->availableLogicalHeight(ExcludeMarginBorderPadding);
+        view().addPercentHeightDescendant(const_cast<RenderBox&>(*this));
+        // FIXME: https://bugs.webkit.org/show_bug.cgi?id=158286 We also need to perform the same percentHeightDescendant treatment to the element which dictates the return value for containingBlock()->availableLogicalHeight() above.
         return std::min(fillAvailableExtent, fillFallbackExtent);
     }
 
     // Use the content box logical height as specified by the style.
-    return cb->adjustContentBoxLogicalHeightForBoxSizing(logicalHeightLength.value());
+    return cb->adjustContentBoxLogicalHeightForBoxSizing(LayoutUnit(logicalHeightLength.value()));
 }
 
 void RenderBox::mapLocalToContainer(const RenderLayerModelObject* repaintContainer, TransformState& transformState, MapCoordinatesFlags mode, bool* wasFixed) const
@@ -1863,15 +2030,14 @@ void RenderBox::mapLocalToContainer(const RenderLayerModelObject* repaintContain
     }
 
     bool containerSkipped;
-    auto o = container(repaintContainer, &containerSkipped);
-    if (!o)
+    RenderElement* container = this->container(repaintContainer, containerSkipped);
+    if (!container)
         return;
 
     bool isFixedPos = style().position() == FixedPosition;
-    bool hasTransform = hasLayer() && layer()->transform();
     // If this box has a transform, it acts as a fixed position container for fixed descendants,
     // and may itself also be fixed position. So propagate 'fixed' up only if this box is fixed position.
-    if (hasTransform && !isFixedPos)
+    if (hasTransform() && !isFixedPos)
         mode &= ~IsFixed;
     else if (isFixedPos)
         mode |= IsFixed;
@@ -1879,12 +2045,12 @@ void RenderBox::mapLocalToContainer(const RenderLayerModelObject* repaintContain
     if (wasFixed)
         *wasFixed = mode & IsFixed;
     
-    LayoutSize containerOffset = offsetFromContainer(o, roundedLayoutPoint(transformState.mappedPoint()));
+    LayoutSize containerOffset = offsetFromContainer(*container, LayoutPoint(transformState.mappedPoint()));
     
-    bool preserve3D = mode & UseTransforms && (o->style().preserves3D() || style().preserves3D());
-    if (mode & UseTransforms && shouldUseTransformFromContainer(o)) {
+    bool preserve3D = mode & UseTransforms && (container->style().preserves3D() || style().preserves3D());
+    if (mode & UseTransforms && shouldUseTransformFromContainer(container)) {
         TransformationMatrix t;
-        getTransformFromContainer(o, containerOffset, t);
+        getTransformFromContainer(container, containerOffset, t);
         transformState.applyTransform(t, preserve3D ? TransformState::AccumulateTransform : TransformState::FlattenTransform);
     } else
         transformState.move(containerOffset.width(), containerOffset.height(), preserve3D ? TransformState::AccumulateTransform : TransformState::FlattenTransform);
@@ -1892,7 +2058,7 @@ void RenderBox::mapLocalToContainer(const RenderLayerModelObject* repaintContain
     if (containerSkipped) {
         // There can't be a transform between repaintContainer and o, because transforms create containers, so it should be safe
         // to just subtract the delta between the repaintContainer and o.
-        LayoutSize containerOffset = repaintContainer->offsetFromAncestorContainer(o);
+        LayoutSize containerOffset = repaintContainer->offsetFromAncestorContainer(*container);
         transformState.move(-containerOffset.width(), -containerOffset.height(), preserve3D ? TransformState::AccumulateTransform : TransformState::FlattenTransform);
         return;
     }
@@ -1901,10 +2067,10 @@ void RenderBox::mapLocalToContainer(const RenderLayerModelObject* repaintContain
 
     // For fixed positioned elements inside out-of-flow named flows, we do not want to
     // map their position further to regions based on their coordinates inside the named flows.
-    if (!o->isOutOfFlowRenderFlowThread() || !fixedPositionedWithNamedFlowContainingBlock())
-        o->mapLocalToContainer(repaintContainer, transformState, mode, wasFixed);
+    if (!container->isOutOfFlowRenderFlowThread() || !fixedPositionedWithNamedFlowContainingBlock())
+        container->mapLocalToContainer(repaintContainer, transformState, mode, wasFixed);
     else
-        o->mapLocalToContainer(toRenderLayerModelObject(o), transformState, mode, wasFixed);
+        container->mapLocalToContainer(downcast<RenderLayerModelObject>(container), transformState, mode, wasFixed);
 }
 
 const RenderObject* RenderBox::pushMappingToContainer(const RenderLayerModelObject* ancestorToStopAt, RenderGeometryMap& geometryMap) const
@@ -1912,33 +2078,31 @@ const RenderObject* RenderBox::pushMappingToContainer(const RenderLayerModelObje
     ASSERT(ancestorToStopAt != this);
 
     bool ancestorSkipped;
-    auto container = this->container(ancestorToStopAt, &ancestorSkipped);
+    RenderElement* container = this->container(ancestorToStopAt, ancestorSkipped);
     if (!container)
-        return 0;
+        return nullptr;
 
     bool isFixedPos = style().position() == FixedPosition;
-    bool hasTransform = hasLayer() && layer()->transform();
-
     LayoutSize adjustmentForSkippedAncestor;
     if (ancestorSkipped) {
-        // There can't be a transform between repaintContainer and o, because transforms create containers, so it should be safe
-        // to just subtract the delta between the ancestor and o.
-        adjustmentForSkippedAncestor = -ancestorToStopAt->offsetFromAncestorContainer(container);
+        // There can't be a transform between repaintContainer and container, because transforms create containers, so it should be safe
+        // to just subtract the delta between the ancestor and container.
+        adjustmentForSkippedAncestor = -ancestorToStopAt->offsetFromAncestorContainer(*container);
     }
 
     bool offsetDependsOnPoint = false;
-    LayoutSize containerOffset = offsetFromContainer(container, LayoutPoint(), &offsetDependsOnPoint);
+    LayoutSize containerOffset = offsetFromContainer(*container, LayoutPoint(), &offsetDependsOnPoint);
 
     bool preserve3D = container->style().preserves3D() || style().preserves3D();
-    if (shouldUseTransformFromContainer(container)) {
+    if (shouldUseTransformFromContainer(container) && (geometryMap.mapCoordinatesFlags() & UseTransforms)) {
         TransformationMatrix t;
         getTransformFromContainer(container, containerOffset, t);
         t.translateRight(adjustmentForSkippedAncestor.width(), adjustmentForSkippedAncestor.height());
         
-        geometryMap.push(this, t, preserve3D, offsetDependsOnPoint, isFixedPos, hasTransform);
+        geometryMap.push(this, t, preserve3D, offsetDependsOnPoint, isFixedPos, hasTransform());
     } else {
         containerOffset += adjustmentForSkippedAncestor;
-        geometryMap.push(this, containerOffset, preserve3D, offsetDependsOnPoint, isFixedPos, hasTransform);
+        geometryMap.push(this, containerOffset, preserve3D, offsetDependsOnPoint, isFixedPos, hasTransform());
     }
     
     return ancestorSkipped ? ancestorToStopAt : container;
@@ -1947,8 +2111,7 @@ const RenderObject* RenderBox::pushMappingToContainer(const RenderLayerModelObje
 void RenderBox::mapAbsoluteToLocalPoint(MapCoordinatesFlags mode, TransformState& transformState) const
 {
     bool isFixedPos = style().position() == FixedPosition;
-    bool hasTransform = hasLayer() && layer()->transform();
-    if (hasTransform && !isFixedPos) {
+    if (hasTransform() && !isFixedPos) {
         // If this box has a transform, it acts as a fixed position container for fixed descendants,
         // and may itself also be fixed position. So propagate 'fixed' up only if this box is fixed position.
         mode &= ~IsFixed;
@@ -1958,40 +2121,26 @@ void RenderBox::mapAbsoluteToLocalPoint(MapCoordinatesFlags mode, TransformState
     RenderBoxModelObject::mapAbsoluteToLocalPoint(mode, transformState);
 }
 
-LayoutSize RenderBox::offsetFromContainer(RenderObject* o, const LayoutPoint& point, bool* offsetDependsOnPoint) const
+LayoutSize RenderBox::offsetFromContainer(RenderElement& renderer, const LayoutPoint&, bool* offsetDependsOnPoint) const
 {
     // A region "has" boxes inside it without being their container. 
-    ASSERT(o == container() || o->isRenderRegion());
+    ASSERT(&renderer == container() || is<RenderRegion>(renderer));
 
     LayoutSize offset;    
     if (isInFlowPositioned())
         offset += offsetForInFlowPosition();
 
-    if (!isInline() || isReplaced()) {
-        if (!style().hasOutOfFlowPosition() && o->hasColumns()) {
-            RenderBlock* block = toRenderBlock(o);
-            LayoutRect columnRect(frameRect());
-            block->adjustStartEdgeForWritingModeIncludingColumns(columnRect);
-            offset += toSize(columnRect.location());
-            LayoutPoint columnPoint = block->flipForWritingModeIncludingColumns(point + offset);
-            offset = toLayoutSize(block->flipForWritingModeIncludingColumns(toLayoutPoint(offset)));
-            o->adjustForColumns(offset, columnPoint);
-            offset = block->flipForWritingMode(offset);
-
-            if (offsetDependsOnPoint)
-                *offsetDependsOnPoint = true;
-        } else
-            offset += topLeftLocationOffset();
-    }
+    if (!isInline() || isReplaced())
+        offset += topLeftLocationOffset();
 
-    if (o->hasOverflowClip())
-        offset -= toRenderBox(o)->scrolledContentOffset();
+    if (is<RenderBox>(renderer))
+        offset -= toLayoutSize(downcast<RenderBox>(renderer).scrollPosition());
 
-    if (style().position() == AbsolutePosition && o->isInFlowPositioned() && o->isRenderInline())
-        offset += toRenderInline(o)->offsetForInFlowPositionedInline(this);
+    if (style().position() == AbsolutePosition && renderer.isInFlowPositioned() && is<RenderInline>(renderer))
+        offset += downcast<RenderInline>(renderer).offsetForInFlowPositionedInline(this);
 
     if (offsetDependsOnPoint)
-        *offsetDependsOnPoint |= o->isRenderFlowThread();
+        *offsetDependsOnPoint |= is<RenderFlowThread>(renderer);
 
     return offset;
 }
@@ -2003,13 +2152,14 @@ std::unique_ptr<InlineElementBox> RenderBox::createInlineBox()
 
 void RenderBox::dirtyLineBoxes(bool fullLayout)
 {
-    if (m_inlineBoxWrapper) {
-        if (fullLayout) {
-            delete m_inlineBoxWrapper;
-            m_inlineBoxWrapper = nullptr;
-        } else
-            m_inlineBoxWrapper->dirtyLineBoxes();
-    }
+    if (!m_inlineBoxWrapper)
+        return;
+    
+    if (fullLayout) {
+        delete m_inlineBoxWrapper;
+        m_inlineBoxWrapper = nullptr;
+    } else
+        m_inlineBoxWrapper->dirtyLineBoxes();
 }
 
 void RenderBox::positionLineBox(InlineElementBox& box)
@@ -2022,9 +2172,9 @@ void RenderBox::positionLineBox(InlineElementBox& box)
             // our object was inline originally, since otherwise it would have ended up underneath
             // the inlines.
             RootInlineBox& rootBox = box.root();
-            rootBox.blockFlow().setStaticInlinePositionForChild(*this, rootBox.lineTopWithLeading(), roundedLayoutUnit(box.logicalLeft()));
+            rootBox.blockFlow().setStaticInlinePositionForChild(*this, rootBox.lineTopWithLeading(), LayoutUnit::fromFloatRound(box.logicalLeft()));
             if (style().hasStaticInlinePosition(box.isHorizontal()))
-                setChildNeedsLayout(MarkOnlyThis); // Just go ahead and mark the positioned object as needing layout, so it will update its position properly.
+                setChildNeedsLayout(MarkOnlyThis); // Just mark the positioned object as needing layout, so it will update its position properly.
         } else {
             // Our object was a block originally, so we make our normal flow position be
             // just below the line box (as though all the inlines that came before us got
@@ -2032,56 +2182,53 @@ void RenderBox::positionLineBox(InlineElementBox& box)
             // in flow).  This value was cached in the y() of the box.
             layer()->setStaticBlockPosition(box.logicalTop());
             if (style().hasStaticBlockPosition(box.isHorizontal()))
-                setChildNeedsLayout(MarkOnlyThis); // Just go ahead and mark the positioned object as needing layout, so it will update its position properly.
+                setChildNeedsLayout(MarkOnlyThis); // Just mark the positioned object as needing layout, so it will update its position properly.
         }
-
-        // Nuke the box.
-        box.removeFromParent();
-        delete &box;
         return;
     }
 
     if (isReplaced()) {
-        setLocation(roundedLayoutPoint(box.topLeft()));
-        // m_inlineBoxWrapper should already be 0. Deleting it is a safeguard against security issues.
-        ASSERT(!m_inlineBoxWrapper);
-        if (m_inlineBoxWrapper)
-            deleteLineBoxWrapper();
-        m_inlineBoxWrapper = &box;
+        setLocation(LayoutPoint(box.topLeft()));
+        setInlineBoxWrapper(&box);
     }
 }
 
 void RenderBox::deleteLineBoxWrapper()
 {
-    if (m_inlineBoxWrapper) {
-        if (!documentBeingDestroyed())
-            m_inlineBoxWrapper->removeFromParent();
-        delete m_inlineBoxWrapper;
-        m_inlineBoxWrapper = nullptr;
-    }
+    if (!m_inlineBoxWrapper)
+        return;
+    
+    if (!renderTreeBeingDestroyed())
+        m_inlineBoxWrapper->removeFromParent();
+    delete m_inlineBoxWrapper;
+    m_inlineBoxWrapper = nullptr;
 }
 
 LayoutRect RenderBox::clippedOverflowRectForRepaint(const RenderLayerModelObject* repaintContainer) const
 {
     if (style().visibility() != VISIBLE && !enclosingLayer()->hasVisibleContent())
         return LayoutRect();
-
     LayoutRect r = visualOverflowRect();
-
     // FIXME: layoutDelta needs to be applied in parts before/after transforms and
     // repaint containers. https://bugs.webkit.org/show_bug.cgi?id=23308
     r.move(view().layoutDelta());
-    
-    // We have to use maximalOutlineSize() because a child might have an outline
-    // that projects outside of our overflowRect.
-    ASSERT(style().outlineSize() <= view().maximalOutlineSize());
-    r.inflate(view().maximalOutlineSize());
-    
-    computeRectForRepaint(repaintContainer, r);
-    return r;
+    return computeRectForRepaint(r, repaintContainer);
 }
 
-void RenderBox::computeRectForRepaint(const RenderLayerModelObject* repaintContainer, LayoutRect& rect, bool fixed) const
+bool RenderBox::shouldApplyClipAndScrollPositionForRepaint(const RenderLayerModelObject* repaintContainer) const
+{
+#if PLATFORM(IOS)
+    if (!repaintContainer || repaintContainer != this)
+        return true;
+
+    return !hasLayer() || !layer()->usesCompositedScrolling();
+#else
+    UNUSED_PARAM(repaintContainer);
+    return true;
+#endif
+}
+
+LayoutRect RenderBox::computeRectForRepaint(const LayoutRect& rect, const RenderLayerModelObject* repaintContainer, RepaintContext context) const
 {
     // The rect we compute at each step is shifted by our x/y offset in the parent container's coordinate space.
     // Only when we cross a writing mode boundary will we have to possibly flipForWritingMode (to convert into a more appropriate
@@ -2091,67 +2238,99 @@ void RenderBox::computeRectForRepaint(const RenderLayerModelObject* repaintConta
     // RenderView::computeRectForRepaint then converts the rect to physical coordinates.  We also convert to
     // physical when we hit a repaintContainer boundary.  Therefore the final rect returned is always in the
     // physical coordinate space of the repaintContainer.
+    LayoutRect adjustedRect = rect;
     const RenderStyle& styleToUse = style();
     // LayoutState is only valid for root-relative, non-fixed position repainting
     if (view().layoutStateEnabled() && !repaintContainer && styleToUse.position() != FixedPosition) {
         LayoutState* layoutState = view().layoutState();
 
         if (layer() && layer()->transform())
-            rect = layer()->transform()->mapRect(pixelSnappedIntRect(rect));
+            adjustedRect = LayoutRect(encloseRectToDevicePixels(layer()->transform()->mapRect(adjustedRect), document().deviceScaleFactor()));
 
         // We can't trust the bits on RenderObject, because this might be called while re-resolving style.
         if (styleToUse.hasInFlowPosition() && layer())
-            rect.move(layer()->offsetForInFlowPosition());
+            adjustedRect.move(layer()->offsetForInFlowPosition());
 
-        rect.moveBy(location());
-        rect.move(layoutState->m_paintOffset);
+        adjustedRect.moveBy(location());
+        adjustedRect.move(layoutState->m_paintOffset);
         if (layoutState->m_clipped)
-            rect.intersect(layoutState->m_clipRect);
-        return;
+            adjustedRect.intersect(layoutState->m_clipRect);
+        return adjustedRect;
     }
 
     if (hasReflection())
-        rect.unite(reflectedRect(rect));
+        adjustedRect.unite(reflectedRect(adjustedRect));
 
     if (repaintContainer == this) {
         if (repaintContainer->style().isFlippedBlocksWritingMode())
-            flipForWritingMode(rect);
-        return;
+            flipForWritingMode(adjustedRect);
+        return adjustedRect;
     }
 
-    bool containerSkipped;
-    auto o = container(repaintContainer, &containerSkipped);
-    if (!o)
-        return;
-
-    if (o->isRenderFlowThread()) {
-        RenderRegion* firstRegion = 0;
-        RenderRegion* lastRegion = 0;
-        toRenderFlowThread(o)->getRegionRangeForBox(this, firstRegion, lastRegion);
-        if (firstRegion)
-            rect.moveBy(firstRegion->flowThreadPortionRect().location());
+    bool repaintContainerIsSkipped;
+    auto* container = this->container(repaintContainer, repaintContainerIsSkipped);
+    if (!container)
+        return adjustedRect;
+    
+    // This code isn't necessary for in-flow RenderFlowThreads.
+    // Don't add the location of the region in the flow thread for absolute positioned
+    // elements because their absolute position already pushes them down through
+    // the regions so adding this here and then adding the topLeft again would cause
+    // us to add the height twice.
+    // The same logic applies for elements flowed directly into the flow thread. Their topLeft member
+    // will already contain the portion rect of the region.
+    EPosition position = styleToUse.position();
+    if (container->isOutOfFlowRenderFlowThread() && position != AbsolutePosition && containingBlock() != flowThreadContainingBlock()) {
+        RenderRegion* firstRegion = nullptr;
+        RenderRegion* lastRegion = nullptr;
+        if (downcast<RenderFlowThread>(*container).getRegionRangeForBox(this, firstRegion, lastRegion))
+            adjustedRect.moveBy(firstRegion->flowThreadPortionRect().location());
     }
 
-    if (isWritingModeRoot() && !isOutOfFlowPositioned())
-        flipForWritingMode(rect);
+    if (isWritingModeRoot()) {
+        if (!isOutOfFlowPositioned() || !context.m_dirtyRectIsFlipped) {
+            flipForWritingMode(adjustedRect);
+            context.m_dirtyRectIsFlipped = true;
+        }
+    }
 
-    LayoutPoint topLeft = rect.location();
-    topLeft.move(locationOffset());
+    LayoutSize locationOffset = this->locationOffset();
+    // FIXME: This is needed as long as RenderWidget snaps to integral size/position.
+    if (isRenderReplaced() && isWidget()) {
+        LayoutSize flooredLocationOffset = toIntSize(flooredIntPoint(locationOffset));
+        adjustedRect.expand(locationOffset - flooredLocationOffset);
+        locationOffset = flooredLocationOffset;
+    }
+
+    if (is<RenderMultiColumnFlowThread>(this)) {
+        // We won't normally run this code. Only when the repaintContainer is null (i.e., we're trying
+        // to get the rect in view coordinates) will we come in here, since normally repaintContainer
+        // will be set and we'll stop at the flow thread. This case is mainly hit by the check for whether
+        // or not images should animate.
+        // FIXME: Just as with offsetFromContainer, we aren't really handling objects that span
+        // multiple columns properly.
+        LayoutPoint physicalPoint(flipForWritingMode(adjustedRect.location()));
+        if (auto* region = downcast<RenderMultiColumnFlowThread>(*this).physicalTranslationFromFlowToRegion((physicalPoint))) {
+            adjustedRect.setLocation(region->flipForWritingMode(physicalPoint));
+            return region->computeRectForRepaint(adjustedRect, repaintContainer, context);
+        }
+    }
 
-    EPosition position = styleToUse.position();
+    LayoutPoint topLeft = adjustedRect.location();
+    topLeft.move(locationOffset);
 
-    // We are now in our parent container's coordinate space.  Apply our transform to obtain a bounding box
+    // We are now in our parent container's coordinate space. Apply our transform to obtain a bounding box
     // in the parent's coordinate space that encloses us.
     if (hasLayer() && layer()->transform()) {
-        fixed = position == FixedPosition;
-        rect = layer()->transform()->mapRect(pixelSnappedIntRect(rect));
-        topLeft = rect.location();
-        topLeft.move(locationOffset());
+        context.m_hasPositionFixedDescendant = position == FixedPosition;
+        adjustedRect = LayoutRect(encloseRectToDevicePixels(layer()->transform()->mapRect(adjustedRect), document().deviceScaleFactor()));
+        topLeft = adjustedRect.location();
+        topLeft.move(locationOffset);
     } else if (position == FixedPosition)
-        fixed = true;
+        context.m_hasPositionFixedDescendant = true;
 
-    if (position == AbsolutePosition && o->isInFlowPositioned() && o->isRenderInline())
-        topLeft += toRenderInline(o)->offsetForInFlowPositionedInline(this);
+    if (position == AbsolutePosition && container->isInFlowPositioned() && is<RenderInline>(*container))
+        topLeft += downcast<RenderInline>(*container).offsetForInFlowPositionedInline(this);
     else if (styleToUse.hasInFlowPosition() && layer()) {
         // Apply the relative position offset when invalidating a rectangle.  The layer
         // is translated, but the render box isn't, so we need to do this to get the
@@ -2159,38 +2338,26 @@ void RenderBox::computeRectForRepaint(const RenderLayerModelObject* repaintConta
         // flag on the RenderObject has been cleared, so use the one on the style().
         topLeft += layer()->offsetForInFlowPosition();
     }
-    
-    if (position != AbsolutePosition && position != FixedPosition && o->hasColumns() && o->isRenderBlockFlow()) {
-        LayoutRect repaintRect(topLeft, rect.size());
-        toRenderBlock(o)->adjustRectForColumns(repaintRect);
-        topLeft = repaintRect.location();
-        rect = repaintRect;
-    }
 
     // FIXME: We ignore the lightweight clipping rect that controls use, since if |o| is in mid-layout,
     // its controlClipRect will be wrong. For overflow clip we use the values cached by the layer.
-    rect.setLocation(topLeft);
-    if (o->hasOverflowClip()) {
-        RenderBox* containerBox = toRenderBox(o);
-#if PLATFORM(IOS)
-        if (!containerBox->layer() || !containerBox->layer()->hasAcceleratedTouchScrolling()) {
-#endif
-        containerBox->applyCachedClipAndScrollOffsetForRepaint(rect);
-        if (rect.isEmpty())
-            return;
-#if PLATFORM(IOS)
-        } 
-#endif
+    adjustedRect.setLocation(topLeft);
+    if (container->hasOverflowClip()) {
+        RenderBox& containerBox = downcast<RenderBox>(*container);
+        if (containerBox.shouldApplyClipAndScrollPositionForRepaint(repaintContainer)) {
+            containerBox.applyCachedClipAndScrollPositionForRepaint(adjustedRect);
+            if (adjustedRect.isEmpty())
+                return adjustedRect;
+        }
     }
 
-    if (containerSkipped) {
-        // If the repaintContainer is below o, then we need to map the rect into repaintContainer's coordinates.
-        LayoutSize containerOffset = repaintContainer->offsetFromAncestorContainer(o);
-        rect.move(-containerOffset);
-        return;
+    if (repaintContainerIsSkipped) {
+        // If the repaintContainer is below container, then we need to map the rect into repaintContainer's coordinates.
+        LayoutSize containerOffset = repaintContainer->offsetFromAncestorContainer(*container);
+        adjustedRect.move(-containerOffset);
+        return adjustedRect;
     }
-
-    o->computeRectForRepaint(repaintContainer, rect, fixed);
+    return container->computeRectForRepaint(adjustedRect, repaintContainer, context);
 }
 
 void RenderBox::repaintDuringLayoutIfMoved(const LayoutRect& oldRect)
@@ -2238,14 +2405,14 @@ void RenderBox::computeLogicalWidthInRegion(LogicalExtentComputedValues& compute
     }
 
     // If layout is limited to a subtree, the subtree root's logical width does not change.
-    if (element() && view().frameView().layoutRoot(true) == this)
+    if (element() && !view().frameView().layoutPending() && view().frameView().layoutRoot() == this)
         return;
 
     // The parent box is flexing us, so it has increased or decreased our
     // width.  Use the width from the style context.
     // FIXME: Account for block-flow in flexible boxes.
     // https://bugs.webkit.org/show_bug.cgi?id=46418
-    if (hasOverrideWidth() && (style().borderFit() == BorderFitLines || parent()->isFlexibleBoxIncludingDeprecated())) {
+    if (hasOverrideLogicalContentWidth() && (isRubyRun() || style().borderFit() == BorderFitLines || (parent()->isFlexibleBoxIncludingDeprecated()))) {
         computedValues.m_extent = overrideLogicalContentWidth() + borderAndPaddingLogicalWidth();
         return;
     }
@@ -2254,15 +2421,18 @@ void RenderBox::computeLogicalWidthInRegion(LogicalExtentComputedValues& compute
     // https://bugs.webkit.org/show_bug.cgi?id=46418
     bool inVerticalBox = parent()->isDeprecatedFlexibleBox() && (parent()->style().boxOrient() == VERTICAL);
     bool stretching = (parent()->style().boxAlign() == BSTRETCH);
+    // FIXME: Stretching is the only reason why we don't want the box to be treated as a replaced element, so we could perhaps
+    // refactor all this logic, not only for flex and grid since alignment is intended to be applied to any block.
     bool treatAsReplaced = shouldComputeSizeAsReplaced() && (!inVerticalBox || !stretching);
+    treatAsReplaced = treatAsReplaced && (!isGridItem() || !hasStretchedLogicalWidth());
 
     const RenderStyle& styleToUse = style();
     Length logicalWidthLength = treatAsReplaced ? Length(computeReplacedLogicalWidth(), Fixed) : styleToUse.logicalWidth();
 
-    RenderBlock* cb = containingBlock();
+    RenderBlock& cb = *containingBlock();
     LayoutUnit containerLogicalWidth = std::max<LayoutUnit>(0, containingBlockLogicalWidthForContentInRegion(region));
-    bool hasPerpendicularContainingBlock = cb->isHorizontalWritingMode() != isHorizontalWritingMode();
-    
+    bool hasPerpendicularContainingBlock = cb.isHorizontalWritingMode() != isHorizontalWritingMode();
+
     if (isInline() && !isInlineBlockOrInlineTable()) {
         // just calculate margins
         computedValues.m_margins.m_start = minimumValueForLength(styleToUse.marginStart(), containerLogicalWidth);
@@ -2272,13 +2442,14 @@ void RenderBox::computeLogicalWidthInRegion(LogicalExtentComputedValues& compute
         return;
     }
 
+    LayoutUnit containerWidthInInlineDirection = containerLogicalWidth;
+    if (hasPerpendicularContainingBlock)
+        containerWidthInInlineDirection = perpendicularContainingBlockLogicalHeight();
+
     // Width calculations
-    if (treatAsReplaced)
+    if (treatAsReplaced) {
         computedValues.m_extent = logicalWidthLength.value() + borderAndPaddingLogicalWidth();
-    else {
-        LayoutUnit containerWidthInInlineDirection = containerLogicalWidth;
-        if (hasPerpendicularContainingBlock)
-            containerWidthInInlineDirection = perpendicularContainingBlockLogicalHeight();
+    } else {
         LayoutUnit preferredWidth = computeLogicalWidthInRegionUsing(MainOrPreferredSize, styleToUse.logicalWidth(), containerWidthInInlineDirection, cb, region);
         computedValues.m_extent = constrainLogicalWidthInRegionByMinMax(preferredWidth, containerWidthInInlineDirection, cb, region);
     }
@@ -2289,18 +2460,24 @@ void RenderBox::computeLogicalWidthInRegion(LogicalExtentComputedValues& compute
         computedValues.m_margins.m_end = minimumValueForLength(styleToUse.marginEnd(), containerLogicalWidth);
     } else {
         LayoutUnit containerLogicalWidthForAutoMargins = containerLogicalWidth;
-        if (avoidsFloats() && cb->containsFloats())
+        if (avoidsFloats() && cb.containsFloats())
             containerLogicalWidthForAutoMargins = containingBlockAvailableLineWidthInRegion(region);
-        bool hasInvertedDirection = cb->style().isLeftToRightDirection() != style().isLeftToRightDirection();
+        bool hasInvertedDirection = cb.style().isLeftToRightDirection() != style().isLeftToRightDirection();
         computeInlineDirectionMargins(cb, containerLogicalWidthForAutoMargins, computedValues.m_extent,
             hasInvertedDirection ? computedValues.m_margins.m_end : computedValues.m_margins.m_start,
             hasInvertedDirection ? computedValues.m_margins.m_start : computedValues.m_margins.m_end);
     }
     
     if (!hasPerpendicularContainingBlock && containerLogicalWidth && containerLogicalWidth != (computedValues.m_extent + computedValues.m_margins.m_start + computedValues.m_margins.m_end)
-        && !isFloating() && !isInline() && !cb->isFlexibleBoxIncludingDeprecated() && !cb->isRenderGrid()) {
-        LayoutUnit newMargin = containerLogicalWidth - computedValues.m_extent - cb->marginStartForChild(*this);
-        bool hasInvertedDirection = cb->style().isLeftToRightDirection() != style().isLeftToRightDirection();
+        && !isFloating() && !isInline() && !cb.isFlexibleBoxIncludingDeprecated()
+#if ENABLE(MATHML)
+        // RenderMathMLBlocks take the size of their content so we must not adjust the margin to fill the container size.
+        && !cb.isRenderMathMLBlock()
+#endif
+        && !cb.isRenderGrid()
+        ) {
+        LayoutUnit newMargin = containerLogicalWidth - computedValues.m_extent - cb.marginStartForChild(*this);
+        bool hasInvertedDirection = cb.style().isLeftToRightDirection() != style().isLeftToRightDirection();
         if (hasInvertedDirection)
             computedValues.m_margins.m_start = newMargin;
         else
@@ -2325,7 +2502,7 @@ LayoutUnit RenderBox::fillAvailableMeasure(LayoutUnit availableLogicalWidth, Lay
 LayoutUnit RenderBox::computeIntrinsicLogicalWidthUsing(Length logicalWidthLength, LayoutUnit availableLogicalWidth, LayoutUnit borderAndPadding) const
 {
     if (logicalWidthLength.type() == FillAvailable)
-        return fillAvailableMeasure(availableLogicalWidth);
+        return std::max(borderAndPadding, fillAvailableMeasure(availableLogicalWidth));
 
     LayoutUnit minLogicalWidth = 0;
     LayoutUnit maxLogicalWidth = 0;
@@ -2348,8 +2525,12 @@ LayoutUnit RenderBox::computeIntrinsicLogicalWidthUsing(Length logicalWidthLengt
 }
 
 LayoutUnit RenderBox::computeLogicalWidthInRegionUsing(SizeType widthType, Length logicalWidth, LayoutUnit availableLogicalWidth,
-    const RenderBlock* cb, RenderRegion* region) const
+    const RenderBlock& cb, RenderRegion* region) const
 {
+    ASSERT(widthType == MinSize || widthType == MainOrPreferredSize || !logicalWidth.isAuto());
+    if (widthType == MinSize && logicalWidth.isAuto())
+        return adjustBorderBoxLogicalWidthForBoxSizing(0);
+
     if (!logicalWidth.isIntrinsicOrAuto()) {
         // FIXME: If the containing block flow is perpendicular to our direction we need to use the available logical height instead.
         return adjustBorderBoxLogicalWidthForBoxSizing(valueForLength(logicalWidth, availableLogicalWidth));
@@ -2362,7 +2543,7 @@ LayoutUnit RenderBox::computeLogicalWidthInRegionUsing(SizeType widthType, Lengt
     LayoutUnit marginEnd = 0;
     LayoutUnit logicalWidthResult = fillAvailableMeasure(availableLogicalWidth, marginStart, marginEnd);
 
-    if (shrinkToAvoidFloats() && cb->containsFloats())
+    if (shrinkToAvoidFloats() && cb.containsFloats())
         logicalWidthResult = std::min(logicalWidthResult, shrinkLogicalWidthToAvoidFloats(marginStart, marginEnd, cb, region));
 
     if (widthType == MainOrPreferredSize && sizesLogicalWidthToFitContent(widthType))
@@ -2373,7 +2554,7 @@ LayoutUnit RenderBox::computeLogicalWidthInRegionUsing(SizeType widthType, Lengt
 static bool flexItemHasStretchAlignment(const RenderBox& flexitem)
 {
     auto parent = flexitem.parent();
-    return flexitem.style().alignSelf() == AlignStretch || (flexitem.style().alignSelf() == AlignAuto && parent->style().alignItems() == AlignStretch);
+    return flexitem.style().resolvedAlignSelf(parent->style(), ItemPositionStretch).position() == ItemPositionStretch;
 }
 
 static bool isStretchingColumnFlexItem(const RenderBox& flexitem)
@@ -2388,13 +2569,37 @@ static bool isStretchingColumnFlexItem(const RenderBox& flexitem)
     return false;
 }
 
+// FIXME: Can/Should we move this inside specific layout classes (flex. grid)? Can we refactor columnFlexItemHasStretchAlignment logic?
+bool RenderBox::hasStretchedLogicalWidth() const
+{
+    auto& style = this->style();
+    if (!style.logicalWidth().isAuto() || style.marginStart().isAuto() || style.marginEnd().isAuto())
+        return false;
+    RenderBlock* containingBlock = this->containingBlock();
+    if (!containingBlock) {
+        // We are evaluating align-self/justify-self, which default to 'normal' for the root element.
+        // The 'normal' value behaves like 'start' except for Flexbox Items, which obviously should have a container.
+        return false;
+    }
+    if (containingBlock->isHorizontalWritingMode() != isHorizontalWritingMode())
+        return style.resolvedAlignSelf(containingBlock->style(), ItemPositionStretch).position() == ItemPositionStretch;
+    return style.resolvedJustifySelf(containingBlock->style(), ItemPositionStretch).position() == ItemPositionStretch;
+}
+
 bool RenderBox::sizesLogicalWidthToFitContent(SizeType widthType) const
 {
+    // Anonymous inline blocks always fill the width of their containing block.
+    if (isAnonymousInlineBlock())
+        return false;
+
     // Marquees in WinIE are like a mixture of blocks and inline-blocks.  They size as though they're blocks,
     // but they allow text to sit on the same line as the marquee.
     if (isFloating() || (isInlineBlockOrInlineTable() && !isHTMLMarquee()))
         return true;
 
+    if (isGridItem())
+        return !hasStretchedLogicalWidth();
+
     // This code may look a bit strange.  Basically width:intrinsic should clamp the size when testing both
     // min-width and width.  max-width is only clamped if it is also intrinsic.
     Length logicalWidth = (widthType == MaxSize) ? style().logicalMaxWidth() : style().logicalWidth();
@@ -2406,15 +2611,21 @@ bool RenderBox::sizesLogicalWidthToFitContent(SizeType widthType) const
     // FIXME: Think about block-flow here.  Need to find out how marquee direction relates to
     // block-flow (as well as how marquee overflow should relate to block flow).
     // https://bugs.webkit.org/show_bug.cgi?id=46472
-    if (parent()->style().overflowX() == OMARQUEE) {
+    if (parent()->isHTMLMarquee()) {
         EMarqueeDirection dir = parent()->style().marqueeDirection();
         if (dir == MAUTO || dir == MFORWARD || dir == MBACKWARD || dir == MLEFT || dir == MRIGHT)
             return true;
     }
 
+#if ENABLE(MATHML)
+    // RenderMathMLBlocks take the size of their content, not of their container.
+    if (parent()->isRenderMathMLBlock())
+        return true;
+#endif
+
     // Flexible box items should shrink wrap, so we lay them out at their intrinsic widths.
-    // In the case of columns that have a stretch alignment, we go ahead and layout at the
-    // stretched size to avoid an extra layout when applying alignment.
+    // In the case of columns that have a stretch alignment, we layout at the stretched size
+    // to avoid an extra layout when applying alignment.
     if (parent()->isFlexibleBox()) {
         // For multiline columns, we need to apply align-content first, so we can't stretch now.
         if (!parent()->style().isColumnFlexDirection() || parent()->style().flexWrap() != FlexNoWrap)
@@ -2434,7 +2645,7 @@ bool RenderBox::sizesLogicalWidthToFitContent(SizeType widthType) const
     // stretching column flexbox.
     // FIXME: Think about block-flow here.
     // https://bugs.webkit.org/show_bug.cgi?id=46473
-    if (logicalWidth.type() == Auto && !isStretchingColumnFlexItem(*this) && element() && (isHTMLInputElement(element()) || element()->hasTagName(selectTag) || element()->hasTagName(buttonTag) || isHTMLTextAreaElement(element()) || element()->hasTagName(legendTag)))
+    if (logicalWidth.type() == Auto && !isStretchingColumnFlexItem(*this) && element() && (is<HTMLInputElement>(*element()) || is<HTMLSelectElement>(*element()) || is<HTMLButtonElement>(*element()) || is<HTMLTextAreaElement>(*element()) || is<HTMLLegendElement>(*element())))
         return true;
 
     if (isHorizontalWritingMode() != containingBlock()->isHorizontalWritingMode())
@@ -2443,9 +2654,9 @@ bool RenderBox::sizesLogicalWidthToFitContent(SizeType widthType) const
     return false;
 }
 
-void RenderBox::computeInlineDirectionMargins(RenderBlock* containingBlock, LayoutUnit containerWidth, LayoutUnit childWidth, LayoutUnit& marginStart, LayoutUnit& marginEnd) const
+void RenderBox::computeInlineDirectionMargins(const RenderBlock& containingBlock, LayoutUnit containerWidth, LayoutUnit childWidth, LayoutUnit& marginStart, LayoutUnit& marginEnd) const
 {
-    const RenderStyle& containingBlockStyle = containingBlock->style();
+    const RenderStyle& containingBlockStyle = containingBlock.style();
     Length marginStartLength = style().marginStartUsing(&containingBlockStyle);
     Length marginEndLength = style().marginEndUsing(&containingBlockStyle);
 
@@ -2458,7 +2669,7 @@ void RenderBox::computeInlineDirectionMargins(RenderBlock* containingBlock, Layo
 
     // Case One: The object is being centered in the containing block's available logical width.
     if ((marginStartLength.isAuto() && marginEndLength.isAuto() && childWidth < containerWidth)
-        || (!marginStartLength.isAuto() && !marginEndLength.isAuto() && containingBlock->style().textAlign() == WEBKIT_CENTER)) {
+        || (!marginStartLength.isAuto() && !marginEndLength.isAuto() && containingBlock.style().textAlign() == WEBKIT_CENTER)) {
         // Other browsers center the margin box for align=center elements so we match them here.
         LayoutUnit marginStartWidth = minimumValueForLength(marginStartLength, containerWidth);
         LayoutUnit marginEndWidth = minimumValueForLength(marginEndLength, containerWidth);
@@ -2478,7 +2689,7 @@ void RenderBox::computeInlineDirectionMargins(RenderBlock* containingBlock, Layo
     // Case Three: The object is being pushed to the end of the containing block's available logical width.
     bool pushToEndFromTextAlign = !marginEndLength.isAuto() && ((!containingBlockStyle.isLeftToRightDirection() && containingBlockStyle.textAlign() == WEBKIT_LEFT)
         || (containingBlockStyle.isLeftToRightDirection() && containingBlockStyle.textAlign() == WEBKIT_RIGHT));
-    if ((marginStartLength.isAuto() && childWidth < containerWidth) || pushToEndFromTextAlign) {
+    if ((marginStartLength.isAuto() || pushToEndFromTextAlign) && childWidth < containerWidth) {
         marginEnd = valueForLength(marginEndLength, containerWidth);
         marginStart = containerWidth - childWidth - marginEnd;
         return;
@@ -2494,7 +2705,7 @@ RenderBoxRegionInfo* RenderBox::renderBoxRegionInfo(RenderRegion* region, Render
 {
     // Make sure nobody is trying to call this with a null region.
     if (!region)
-        return 0;
+        return nullptr;
 
     // If we have computed our width in this region already, it will be cached, and we can
     // just return it.
@@ -2506,17 +2717,17 @@ RenderBoxRegionInfo* RenderBox::renderBoxRegionInfo(RenderRegion* region, Render
     // FIXME: For now we limit this computation to normal RenderBlocks. Future patches will expand
     // support to cover all boxes.
     RenderFlowThread* flowThread = flowThreadContainingBlock();
-    if (isRenderFlowThread() || !flowThread || !canHaveBoxInfoInRegion() || flowThread->style().writingMode() != style().writingMode())
-        return 0;
+    if (isRenderFlowThread() || !is<RenderNamedFlowThread>(flowThread) || !canHaveBoxInfoInRegion() || flowThread->style().writingMode() != style().writingMode())
+        return nullptr;
 
     LogicalExtentComputedValues computedValues;
     computeLogicalWidthInRegion(computedValues, region);
 
     // Now determine the insets based off where this object is supposed to be positioned.
-    RenderBlock* cb = containingBlock();
-    RenderRegion* clampedContainingBlockRegion = cb->clampToStartAndEndRegions(region);
-    RenderBoxRegionInfo* containingBlockInfo = cb->renderBoxRegionInfo(clampedContainingBlockRegion);
-    LayoutUnit containingBlockLogicalWidth = cb->logicalWidth();
+    RenderBlock& cb = *containingBlock();
+    RenderRegion* clampedContainingBlockRegion = cb.clampToStartAndEndRegions(region);
+    RenderBoxRegionInfo* containingBlockInfo = cb.renderBoxRegionInfo(clampedContainingBlockRegion);
+    LayoutUnit containingBlockLogicalWidth = cb.logicalWidth();
     LayoutUnit containingBlockLogicalWidthInRegion = containingBlockInfo ? containingBlockInfo->logicalWidth() : containingBlockLogicalWidth;
     
     LayoutUnit marginStartInRegion = computedValues.m_margins.m_start;
@@ -2531,15 +2742,15 @@ RenderBoxRegionInfo* RenderBox::renderBoxRegionInfo(RenderRegion* region, Render
 
     LayoutUnit logicalLeftOffset = 0;
     
-    if (!isOutOfFlowPositioned() && avoidsFloats() && cb->containsFloats()) {
-        LayoutUnit startPositionDelta = cb->computeStartPositionDeltaForChildAvoidingFloats(*this, marginStartInRegion, region);
-        if (cb->style().isLeftToRightDirection())
+    if (!isOutOfFlowPositioned() && avoidsFloats() && cb.containsFloats()) {
+        LayoutUnit startPositionDelta = cb.computeStartPositionDeltaForChildAvoidingFloats(*this, marginStartInRegion, region);
+        if (cb.style().isLeftToRightDirection())
             logicalLeftDelta += startPositionDelta;
         else
             logicalRightDelta += startPositionDelta;
     }
 
-    if (cb->style().isLeftToRightDirection())
+    if (cb.style().isLeftToRightDirection())
         logicalLeftOffset += logicalLeftDelta;
     else
         logicalLeftOffset -= (widthDelta + logicalRightDelta);
@@ -2583,33 +2794,32 @@ static bool shouldFlipBeforeAfterMargins(const RenderStyle& containingBlockStyle
 
 void RenderBox::updateLogicalHeight()
 {
-    LogicalExtentComputedValues computedValues;
-    computeLogicalHeight(logicalHeight(), logicalTop(), computedValues);
-
+    auto computedValues = computeLogicalHeight(logicalHeight(), logicalTop());
     setLogicalHeight(computedValues.m_extent);
     setLogicalTop(computedValues.m_position);
     setMarginBefore(computedValues.m_margins.m_before);
     setMarginAfter(computedValues.m_margins.m_after);
 }
 
-void RenderBox::computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logicalTop, LogicalExtentComputedValues& computedValues) const
+RenderBox::LogicalExtentComputedValues RenderBox::computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logicalTop) const
 {
+    LogicalExtentComputedValues computedValues;
     computedValues.m_extent = logicalHeight;
     computedValues.m_position = logicalTop;
 
     // Cell height is managed by the table and inline non-replaced elements do not support a height property.
     if (isTableCell() || (isInline() && !isReplaced()))
-        return;
+        return computedValues;
 
     Length h;
     if (isOutOfFlowPositioned())
         computePositionedLogicalHeight(computedValues);
     else {
-        RenderBlock* cb = containingBlock();
-        bool hasPerpendicularContainingBlock = cb->isHorizontalWritingMode() != isHorizontalWritingMode();
+        RenderBlock& cb = *containingBlock();
+        bool hasPerpendicularContainingBlock = cb.isHorizontalWritingMode() != isHorizontalWritingMode();
     
         if (!hasPerpendicularContainingBlock) {
-            bool shouldFlipBeforeAfter = cb->style().writingMode() != style().writingMode();
+            bool shouldFlipBeforeAfter = cb.style().writingMode() != style().writingMode();
             computeBlockDirectionMargins(cb,
                 shouldFlipBeforeAfter ? computedValues.m_margins.m_after : computedValues.m_margins.m_before,
                 shouldFlipBeforeAfter ? computedValues.m_margins.m_before : computedValues.m_margins.m_after);
@@ -2618,12 +2828,12 @@ void RenderBox::computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logica
         // For tables, calculate margins only.
         if (isTable()) {
             if (hasPerpendicularContainingBlock) {
-                bool shouldFlipBeforeAfter = shouldFlipBeforeAfterMargins(cb->style(), &style());
+                bool shouldFlipBeforeAfter = shouldFlipBeforeAfterMargins(cb.style(), &style());
                 computeInlineDirectionMargins(cb, containingBlockLogicalWidthForContent(), computedValues.m_extent,
                     shouldFlipBeforeAfter ? computedValues.m_margins.m_after : computedValues.m_margins.m_before,
                     shouldFlipBeforeAfter ? computedValues.m_margins.m_before : computedValues.m_margins.m_after);
             }
-            return;
+            return computedValues;
         }
 
         // FIXME: Account for block-flow in flexible boxes.
@@ -2637,9 +2847,9 @@ void RenderBox::computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logica
         // grab our cached flexible height.
         // FIXME: Account for block-flow in flexible boxes.
         // https://bugs.webkit.org/show_bug.cgi?id=46418
-        if (hasOverrideHeight() && parent()->isFlexibleBoxIncludingDeprecated())
+        if (hasOverrideLogicalContentHeight() && (parent()->isFlexibleBoxIncludingDeprecated() || parent()->isRenderGrid())) {
             h = Length(overrideLogicalContentHeight(), Fixed);
-        else if (treatAsReplaced)
+        } else if (treatAsReplaced)
             h = Length(computeReplacedLogicalHeight(), Fixed);
         else {
             h = style().logicalHeight();
@@ -2649,29 +2859,29 @@ void RenderBox::computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logica
         // Block children of horizontal flexible boxes fill the height of the box.
         // FIXME: Account for block-flow in flexible boxes.
         // https://bugs.webkit.org/show_bug.cgi?id=46418
-        if (h.isAuto() && parent()->isDeprecatedFlexibleBox() && parent()->style().boxOrient() == HORIZONTAL
-                && parent()->isStretchingChildren()) {
+        if (h.isAuto() && is<RenderDeprecatedFlexibleBox>(*parent()) && parent()->style().boxOrient() == HORIZONTAL
+                && downcast<RenderDeprecatedFlexibleBox>(*parent()).isStretchingChildren()) {
             h = Length(parentBox()->contentLogicalHeight() - marginBefore() - marginAfter() - borderAndPaddingLogicalHeight(), Fixed);
             checkMinMaxHeight = false;
         }
 
         LayoutUnit heightResult;
         if (checkMinMaxHeight) {
-            heightResult = computeLogicalHeightUsing(style().logicalHeight());
-            if (heightResult == -1)
-                heightResult = computedValues.m_extent;
-            heightResult = constrainLogicalHeightByMinMax(heightResult);
+            LayoutUnit intrinsicHeight = computedValues.m_extent - borderAndPaddingLogicalHeight();
+            heightResult = computeLogicalHeightUsing(MainOrPreferredSize, style().logicalHeight(), intrinsicHeight).value_or(computedValues.m_extent);
+            heightResult = constrainLogicalHeightByMinMax(heightResult, intrinsicHeight);
         } else {
             // The only times we don't check min/max height are when a fixed length has
             // been given as an override.  Just use that.  The value has already been adjusted
             // for box-sizing.
+            ASSERT(h.isFixed());
             heightResult = h.value() + borderAndPaddingLogicalHeight();
         }
 
         computedValues.m_extent = heightResult;
-        
+
         if (hasPerpendicularContainingBlock) {
-            bool shouldFlipBeforeAfter = shouldFlipBeforeAfterMargins(cb->style(), &style());
+            bool shouldFlipBeforeAfter = shouldFlipBeforeAfterMargins(cb.style(), &style());
             computeInlineDirectionMargins(cb, containingBlockLogicalWidthForContent(), heightResult,
                     shouldFlipBeforeAfter ? computedValues.m_margins.m_after : computedValues.m_margins.m_before,
                     shouldFlipBeforeAfter ? computedValues.m_margins.m_before : computedValues.m_margins.m_after);
@@ -2683,66 +2893,105 @@ void RenderBox::computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logica
     // is specified. When we're printing, we also need this quirk if the body or root has a percentage 
     // height since we don't set a height in RenderView when we're printing. So without this quirk, the 
     // height has nothing to be a percentage of, and it ends up being 0. That is bad.
-    bool paginatedContentNeedsBaseHeight = document().printing() && h.isPercent()
-        && (isRoot() || (isBody() && document().documentElement()->renderer()->style().logicalHeight().isPercent())) && !isInline();
+    bool paginatedContentNeedsBaseHeight = document().printing() && h.isPercentOrCalculated()
+        && (isDocumentElementRenderer() || (isBody() && document().documentElement()->renderer()->style().logicalHeight().isPercentOrCalculated())) && !isInline();
     if (stretchesToViewport() || paginatedContentNeedsBaseHeight) {
         LayoutUnit margins = collapsedMarginBefore() + collapsedMarginAfter();
         LayoutUnit visibleHeight = view().pageOrViewLogicalHeight();
-        if (isRoot())
+        if (isDocumentElementRenderer())
             computedValues.m_extent = std::max(computedValues.m_extent, visibleHeight - margins);
         else {
             LayoutUnit marginsBordersPadding = margins + parentBox()->marginBefore() + parentBox()->marginAfter() + parentBox()->borderAndPaddingLogicalHeight();
             computedValues.m_extent = std::max(computedValues.m_extent, visibleHeight - marginsBordersPadding);
         }
     }
+    return computedValues;
 }
 
-LayoutUnit RenderBox::computeLogicalHeightUsing(const Length& height) const
+std::optional<LayoutUnit> RenderBox::computeLogicalHeightUsing(SizeType heightType, const Length& height, std::optional<LayoutUnit> intrinsicContentHeight) const
 {
-    LayoutUnit logicalHeight = computeContentAndScrollbarLogicalHeightUsing(height);
-    if (logicalHeight != -1)
-        logicalHeight = adjustBorderBoxLogicalHeightForBoxSizing(logicalHeight);
-    return logicalHeight;
+    if (std::optional<LayoutUnit> logicalHeight = computeContentAndScrollbarLogicalHeightUsing(heightType, height, intrinsicContentHeight))
+        return adjustBorderBoxLogicalHeightForBoxSizing(logicalHeight.value());
+    return std::nullopt;
+}
+
+std::optional<LayoutUnit> RenderBox::computeContentLogicalHeight(SizeType heightType, const Length& height, std::optional<LayoutUnit> intrinsicContentHeight) const
+{
+    if (std::optional<LayoutUnit> heightIncludingScrollbar = computeContentAndScrollbarLogicalHeightUsing(heightType, height, intrinsicContentHeight))
+        return std::max<LayoutUnit>(0, adjustContentBoxLogicalHeightForBoxSizing(heightIncludingScrollbar) - scrollbarLogicalHeight());
+    return std::nullopt;
 }
 
-LayoutUnit RenderBox::computeContentLogicalHeight(const Length& height) const
+std::optional<LayoutUnit> RenderBox::computeIntrinsicLogicalContentHeightUsing(Length logicalHeightLength, std::optional<LayoutUnit> intrinsicContentHeight, LayoutUnit borderAndPadding) const
 {
-    LayoutUnit heightIncludingScrollbar = computeContentAndScrollbarLogicalHeightUsing(height);
-    if (heightIncludingScrollbar == -1)
-        return -1;
-    return std::max<LayoutUnit>(0, adjustContentBoxLogicalHeightForBoxSizing(heightIncludingScrollbar) - scrollbarLogicalHeight());
+    // FIXME: The CSS sizing spec is considering changing what min-content/max-content should resolve to.
+    // If that happens, this code will have to change.
+    if (logicalHeightLength.isMinContent() || logicalHeightLength.isMaxContent() || logicalHeightLength.isFitContent()) {
+        if (!intrinsicContentHeight)
+            return intrinsicContentHeight;
+        if (style().boxSizing() == BORDER_BOX)
+            return intrinsicContentHeight.value() + borderAndPaddingLogicalHeight();
+        return intrinsicContentHeight;
+    }
+    if (logicalHeightLength.isFillAvailable())
+        return containingBlock()->availableLogicalHeight(ExcludeMarginBorderPadding) - borderAndPadding;
+    ASSERT_NOT_REACHED();
+    return LayoutUnit(0);
 }
 
-LayoutUnit RenderBox::computeContentAndScrollbarLogicalHeightUsing(const Length& height) const
+std::optional<LayoutUnit> RenderBox::computeContentAndScrollbarLogicalHeightUsing(SizeType heightType, const Length& height, std::optional<LayoutUnit> intrinsicContentHeight) const
 {
+    if (height.isAuto())
+        return heightType == MinSize ? std::optional<LayoutUnit>(0) : std::nullopt;
+    // FIXME: The CSS sizing spec is considering changing what min-content/max-content should resolve to.
+    // If that happens, this code will have to change.
+    if (height.isIntrinsic())
+        return computeIntrinsicLogicalContentHeightUsing(height, intrinsicContentHeight, borderAndPaddingLogicalHeight());
     if (height.isFixed())
-        return height.value();
-    if (height.isPercent())
+        return LayoutUnit(height.value());
+    if (height.isPercentOrCalculated())
         return computePercentageLogicalHeight(height);
-    if (height.isViewportPercentage())
-        return valueForLength(height, 0);
-    return -1;
+    return std::nullopt;
 }
 
-bool RenderBox::skipContainingBlockForPercentHeightCalculation(const RenderBox* containingBlock) const
+bool RenderBox::skipContainingBlockForPercentHeightCalculation(const RenderBox& containingBlock, bool isPerpendicularWritingMode) const
 {
+    // Flow threads for multicol or paged overflow should be skipped. They are invisible to the DOM,
+    // and percent heights of children should be resolved against the multicol or paged container.
+    if (containingBlock.isInFlowRenderFlowThread() && !isPerpendicularWritingMode)
+        return true;
+
     // For quirks mode and anonymous blocks, we skip auto-height containingBlocks when computing percentages.
     // For standards mode, we treat the percentage as auto if it has an auto-height containing block.
-    if (!document().inQuirksMode() && !containingBlock->isAnonymousBlock())
+    if (!document().inQuirksMode() && !containingBlock.isAnonymousBlock())
         return false;
-    return !containingBlock->isTableCell() && !containingBlock->isOutOfFlowPositioned() && containingBlock->style().logicalHeight().isAuto() && isHorizontalWritingMode() == containingBlock->isHorizontalWritingMode();
+    return !containingBlock.isTableCell() && !containingBlock.isOutOfFlowPositioned() && containingBlock.style().logicalHeight().isAuto() && isHorizontalWritingMode() == containingBlock.isHorizontalWritingMode();
 }
 
-LayoutUnit RenderBox::computePercentageLogicalHeight(const Length& height) const
+static bool tableCellShouldHaveZeroInitialSize(const RenderBlock& block, bool scrollsOverflowY)
 {
-    LayoutUnit availableHeight = -1;
-    
+    // Normally we would let the cell size intrinsically, but scrolling overflow has to be
+    // treated differently, since WinIE lets scrolled overflow regions shrink as needed.
+    // While we can't get all cases right, we can at least detect when the cell has a specified
+    // height or when the table has a specified height. In these cases we want to initially have
+    // no size and allow the flexing of the table or the cell to its specified height to cause us
+    // to grow to fill the space. This could end up being wrong in some cases, but it is
+    // preferable to the alternative (sizing intrinsically and making the row end up too big).
+    const RenderTableCell& cell = downcast<RenderTableCell>(block);
+    return scrollsOverflowY && (!cell.style().logicalHeight().isAuto() || !cell.table()->style().logicalHeight().isAuto());
+}
+
+std::optional<LayoutUnit> RenderBox::computePercentageLogicalHeight(const Length& height) const
+{
+    std::optional<LayoutUnit> availableHeight;
+
     bool skippedAutoHeightContainingBlock = false;
     RenderBlock* cb = containingBlock();
     const RenderBox* containingBlockChild = this;
     LayoutUnit rootMarginBorderPaddingHeight = 0;
-    while (!cb->isRenderView() && skipContainingBlockForPercentHeightCalculation(cb)) {
-        if (cb->isBody() || cb->isRoot())
+    bool isHorizontal = isHorizontalWritingMode();
+    while (cb && !is<RenderView>(*cb) && skipContainingBlockForPercentHeightCalculation(*cb, isHorizontal != cb->isHorizontalWritingMode())) {
+        if (cb->isBody() || cb->isDocumentElementRenderer())
             rootMarginBorderPaddingHeight += cb->marginBefore() + cb->marginAfter() + cb->borderAndPaddingLogicalHeight();
         skippedAutoHeightContainingBlock = true;
         containingBlockChild = cb;
@@ -2758,72 +3007,49 @@ LayoutUnit RenderBox::computePercentageLogicalHeight(const Length& height) const
 
     bool includeBorderPadding = isTable();
 
-    if (isHorizontalWritingMode() != cb->isHorizontalWritingMode())
+    if (isHorizontal != cb->isHorizontalWritingMode())
         availableHeight = containingBlockChild->containingBlockLogicalWidthForContent();
     else if (hasOverrideContainingBlockLogicalHeight())
         availableHeight = overrideContainingBlockContentLogicalHeight();
-    else if (cb->isTableCell()) {
+    else if (cb->isGridItem() && cb->hasOverrideLogicalContentHeight())
+        availableHeight = cb->overrideLogicalContentHeight();
+    else if (is<RenderTableCell>(*cb)) {
         if (!skippedAutoHeightContainingBlock) {
             // Table cells violate what the CSS spec says to do with heights. Basically we
             // don't care if the cell specified a height or not. We just always make ourselves
             // be a percentage of the cell's current content height.
-            if (!cb->hasOverrideHeight()) {
-                // Normally we would let the cell size intrinsically, but scrolling overflow has to be
-                // treated differently, since WinIE lets scrolled overflow regions shrink as needed.
-                // While we can't get all cases right, we can at least detect when the cell has a specified
-                // height or when the table has a specified height. In these cases we want to initially have
-                // no size and allow the flexing of the table or the cell to its specified height to cause us
-                // to grow to fill the space. This could end up being wrong in some cases, but it is
-                // preferable to the alternative (sizing intrinsically and making the row end up too big).
-                RenderTableCell* cell = toRenderTableCell(cb);
-                if (scrollsOverflowY() && (!cell->style().logicalHeight().isAuto() || !cell->table()->style().logicalHeight().isAuto()))
-                    return 0;
-                return -1;
-            }
+            if (!cb->hasOverrideLogicalContentHeight())
+                return tableCellShouldHaveZeroInitialSize(*cb, scrollsOverflowY()) ? std::optional<LayoutUnit>(0) : std::nullopt;
+
             availableHeight = cb->overrideLogicalContentHeight();
             includeBorderPadding = true;
         }
     } else if (cbstyle.logicalHeight().isFixed()) {
-        LayoutUnit contentBoxHeight = cb->adjustContentBoxLogicalHeightForBoxSizing(cbstyle.logicalHeight().value());
-        availableHeight = std::max<LayoutUnit>(0, cb->constrainContentBoxLogicalHeightByMinMax(contentBoxHeight - cb->scrollbarLogicalHeight()));
-    } else if (cbstyle.logicalHeight().isPercent() && !isOutOfFlowPositionedWithSpecifiedHeight) {
+        LayoutUnit contentBoxHeight = cb->adjustContentBoxLogicalHeightForBoxSizing(LayoutUnit(cbstyle.logicalHeight().value()));
+        availableHeight = std::max<LayoutUnit>(0, cb->constrainContentBoxLogicalHeightByMinMax(contentBoxHeight - cb->scrollbarLogicalHeight(), std::nullopt));
+    } else if (cbstyle.logicalHeight().isPercentOrCalculated() && !isOutOfFlowPositionedWithSpecifiedHeight) {
         // We need to recur and compute the percentage height for our containing block.
-        LayoutUnit heightWithScrollbar = cb->computePercentageLogicalHeight(cbstyle.logicalHeight());
-        if (heightWithScrollbar != -1) {
+        if (std::optional<LayoutUnit> heightWithScrollbar = cb->computePercentageLogicalHeight(cbstyle.logicalHeight())) {
             LayoutUnit contentBoxHeightWithScrollbar = cb->adjustContentBoxLogicalHeightForBoxSizing(heightWithScrollbar);
             // We need to adjust for min/max height because this method does not
             // handle the min/max of the current block, its caller does. So the
             // return value from the recursive call will not have been adjusted
             // yet.
-            LayoutUnit contentBoxHeight = cb->constrainContentBoxLogicalHeightByMinMax(contentBoxHeightWithScrollbar - cb->scrollbarLogicalHeight());
-            availableHeight = std::max<LayoutUnit>(0, contentBoxHeight);
-        }
-    } else if (cbstyle.logicalHeight().isViewportPercentage()) {
-        LayoutUnit heightWithScrollbar = valueForLength(cbstyle.logicalHeight(), 0, &view());
-        if (heightWithScrollbar != -1) {
-            LayoutUnit contentBoxHeightWithScrollbar = cb->adjustContentBoxLogicalHeightForBoxSizing(heightWithScrollbar);
-            // We need to adjust for min/max height because this method does 
-            // not handle the min/max of the current block, its caller does.
-            // So the return value from the recursive call will not have been
-            // adjusted yet.
-            LayoutUnit contentBoxHeight = cb->constrainContentBoxLogicalHeightByMinMax(contentBoxHeightWithScrollbar - cb->scrollbarLogicalHeight());
+            LayoutUnit contentBoxHeight = cb->constrainContentBoxLogicalHeightByMinMax(contentBoxHeightWithScrollbar - cb->scrollbarLogicalHeight(), std::nullopt);
             availableHeight = std::max<LayoutUnit>(0, contentBoxHeight);
         }
     } else if (isOutOfFlowPositionedWithSpecifiedHeight) {
         // Don't allow this to affect the block' height() member variable, since this
         // can get called while the block is still laying out its kids.
-        LogicalExtentComputedValues computedValues;
-        cb->computeLogicalHeight(cb->logicalHeight(), 0, computedValues);
+        auto computedValues = cb->computeLogicalHeight(cb->logicalHeight(), 0);
         availableHeight = computedValues.m_extent - cb->borderAndPaddingLogicalHeight() - cb->scrollbarLogicalHeight();
     } else if (cb->isRenderView())
         availableHeight = view().pageOrViewLogicalHeight();
 
-    if (availableHeight == -1)
+    if (!availableHeight)
         return availableHeight;
 
-    availableHeight -= rootMarginBorderPaddingHeight;
-
-    LayoutUnit result = valueForLength(height, availableHeight);
+    LayoutUnit result = valueForLength(height, availableHeight.value() - rootMarginBorderPaddingHeight);
     if (includeBorderPadding) {
         // FIXME: Table cells should default to box-sizing: border-box so we can avoid this hack.
         // It is necessary to use the border-box to match WinIE's broken
@@ -2837,18 +3063,26 @@ LayoutUnit RenderBox::computePercentageLogicalHeight(const Length& height) const
 
 LayoutUnit RenderBox::computeReplacedLogicalWidth(ShouldComputePreferred shouldComputePreferred) const
 {
-    return computeReplacedLogicalWidthRespectingMinMaxWidth(computeReplacedLogicalWidthUsing(style().logicalWidth()), shouldComputePreferred);
+    return computeReplacedLogicalWidthRespectingMinMaxWidth(computeReplacedLogicalWidthUsing(MainOrPreferredSize, style().logicalWidth()), shouldComputePreferred);
 }
 
 LayoutUnit RenderBox::computeReplacedLogicalWidthRespectingMinMaxWidth(LayoutUnit logicalWidth, ShouldComputePreferred shouldComputePreferred) const
 {
-    LayoutUnit minLogicalWidth = (shouldComputePreferred == ComputePreferred && style().logicalMinWidth().isPercent()) || style().logicalMinWidth().isUndefined() ? logicalWidth : computeReplacedLogicalWidthUsing(style().logicalMinWidth());
-    LayoutUnit maxLogicalWidth = (shouldComputePreferred == ComputePreferred && style().logicalMaxWidth().isPercent()) || style().logicalMaxWidth().isUndefined() ? logicalWidth : computeReplacedLogicalWidthUsing(style().logicalMaxWidth());
+    auto& logicalMinWidth = style().logicalMinWidth();
+    auto& logicalMaxWidth = style().logicalMaxWidth();
+    bool useLogicalWidthForMinWidth = (shouldComputePreferred == ComputePreferred && logicalMinWidth.isPercentOrCalculated()) || logicalMinWidth.isUndefined();
+    bool useLogicalWidthForMaxWidth = (shouldComputePreferred == ComputePreferred && logicalMaxWidth.isPercentOrCalculated()) || logicalMaxWidth.isUndefined();
+    auto minLogicalWidth =  useLogicalWidthForMinWidth ? logicalWidth : computeReplacedLogicalWidthUsing(MinSize, logicalMinWidth);
+    auto maxLogicalWidth =  useLogicalWidthForMaxWidth ? logicalWidth : computeReplacedLogicalWidthUsing(MaxSize, logicalMaxWidth);
     return std::max(minLogicalWidth, std::min(logicalWidth, maxLogicalWidth));
 }
 
-LayoutUnit RenderBox::computeReplacedLogicalWidthUsing(Length logicalWidth) const
+LayoutUnit RenderBox::computeReplacedLogicalWidthUsing(SizeType widthType, Length logicalWidth) const
 {
+    ASSERT(widthType == MinSize || widthType == MainOrPreferredSize || !logicalWidth.isAuto());
+    if (widthType == MinSize && logicalWidth.isAuto())
+        return adjustContentBoxLogicalWidthForBoxSizing(0);
+
     switch (logicalWidth.type()) {
         case Fixed:
             return adjustContentBoxLogicalWidthForBoxSizing(logicalWidth.value());
@@ -2858,11 +3092,6 @@ LayoutUnit RenderBox::computeReplacedLogicalWidthUsing(Length logicalWidth) cons
             LayoutUnit availableLogicalWidth = 0;
             return computeIntrinsicLogicalWidthUsing(logicalWidth, availableLogicalWidth, borderAndPaddingLogicalWidth()) - borderAndPaddingLogicalWidth();
         }
-        case ViewportPercentageWidth:
-        case ViewportPercentageHeight:
-        case ViewportPercentageMin:
-        case ViewportPercentageMax:
-            return adjustContentBoxLogicalWidthForBoxSizing(valueForLength(logicalWidth, 0));
         case FitContent:
         case FillAvailable:
         case Percent: 
@@ -2870,13 +3099,13 @@ LayoutUnit RenderBox::computeReplacedLogicalWidthUsing(Length logicalWidth) cons
             // FIXME: containingBlockLogicalWidthForContent() is wrong if the replaced element's block-flow is perpendicular to the
             // containing block's block-flow.
             // https://bugs.webkit.org/show_bug.cgi?id=46496
-            const LayoutUnit cw = isOutOfFlowPositioned() ? containingBlockLogicalWidthForPositioned(toRenderBoxModelObject(container())) : containingBlockLogicalWidthForContent();
+            const LayoutUnit cw = isOutOfFlowPositioned() ? containingBlockLogicalWidthForPositioned(downcast<RenderBoxModelObject>(*container())) : containingBlockLogicalWidthForContent();
             Length containerLogicalWidth = containingBlock()->style().logicalWidth();
             // FIXME: Handle cases when containing block width is calculated or viewport percent.
             // https://bugs.webkit.org/show_bug.cgi?id=91071
             if (logicalWidth.isIntrinsic())
                 return computeIntrinsicLogicalWidthUsing(logicalWidth, cw, borderAndPaddingLogicalWidth()) - borderAndPaddingLogicalWidth();
-            if (cw > 0 || (!cw && (containerLogicalWidth.isFixed() || containerLogicalWidth.isPercent())))
+            if (cw > 0 || (!cw && (containerLogicalWidth.isFixed() || containerLogicalWidth.isPercentOrCalculated())))
                 return adjustContentBoxLogicalWidthForBoxSizing(minimumValueForLength(logicalWidth, cw));
         }
         FALLTHROUGH;
@@ -2892,41 +3121,49 @@ LayoutUnit RenderBox::computeReplacedLogicalWidthUsing(Length logicalWidth) cons
     return 0;
 }
 
-LayoutUnit RenderBox::computeReplacedLogicalHeight() const
+LayoutUnit RenderBox::computeReplacedLogicalHeight(std::optional<LayoutUnit>) const
 {
-    return computeReplacedLogicalHeightRespectingMinMaxHeight(computeReplacedLogicalHeightUsing(style().logicalHeight()));
+    return computeReplacedLogicalHeightRespectingMinMaxHeight(computeReplacedLogicalHeightUsing(MainOrPreferredSize, style().logicalHeight()));
 }
 
 LayoutUnit RenderBox::computeReplacedLogicalHeightRespectingMinMaxHeight(LayoutUnit logicalHeight) const
 {
-    LayoutUnit minLogicalHeight = computeReplacedLogicalHeightUsing(style().logicalMinHeight());
-    LayoutUnit maxLogicalHeight = style().logicalMaxHeight().isUndefined() ? logicalHeight : computeReplacedLogicalHeightUsing(style().logicalMaxHeight());
+    LayoutUnit minLogicalHeight = computeReplacedLogicalHeightUsing(MinSize, style().logicalMinHeight());
+    LayoutUnit maxLogicalHeight = style().logicalMaxHeight().isUndefined() ? logicalHeight : computeReplacedLogicalHeightUsing(MaxSize, style().logicalMaxHeight());
     return std::max(minLogicalHeight, std::min(logicalHeight, maxLogicalHeight));
 }
 
-LayoutUnit RenderBox::computeReplacedLogicalHeightUsing(Length logicalHeight) const
+LayoutUnit RenderBox::computeReplacedLogicalHeightUsing(SizeType heightType, Length logicalHeight) const
 {
+    ASSERT(heightType == MinSize || heightType == MainOrPreferredSize || !logicalHeight.isAuto());
+    if (heightType == MinSize && logicalHeight.isAuto())
+        return adjustContentBoxLogicalHeightForBoxSizing(std::optional<LayoutUnit>(0));
+
     switch (logicalHeight.type()) {
         case Fixed:
-            return adjustContentBoxLogicalHeightForBoxSizing(logicalHeight.value());
+            return adjustContentBoxLogicalHeightForBoxSizing(LayoutUnit(logicalHeight.value()));
         case Percent:
         case Calculated:
         {
-            auto cb = isOutOfFlowPositioned() ? container() : containingBlock();
-            while (cb->isAnonymous() && !cb->isRenderView()) {
-                cb = cb->containingBlock();
-                toRenderBlock(cb)->addPercentHeightDescendant(const_cast<RenderBox&>(*this));
+            auto* container = isOutOfFlowPositioned() ? this->container() : containingBlock();
+            while (container && container->isAnonymous()) {
+                // Stop at rendering context root.
+                if (is<RenderView>(*container) || is<RenderNamedFlowThread>(*container))
+                    break;
+                container = container->containingBlock();
+                downcast<RenderBlock>(*container).addPercentHeightDescendant(const_cast<RenderBox&>(*this));
             }
 
             // FIXME: This calculation is not patched for block-flow yet.
             // https://bugs.webkit.org/show_bug.cgi?id=46500
-            if (cb->isOutOfFlowPositioned() && cb->style().height().isAuto() && !(cb->style().top().isAuto() || cb->style().bottom().isAuto())) {
-                ASSERT_WITH_SECURITY_IMPLICATION(cb->isRenderBlock());
-                RenderBlock* block = toRenderBlock(cb);
-                LogicalExtentComputedValues computedValues;
-                block->computeLogicalHeight(block->logicalHeight(), 0, computedValues);
-                LayoutUnit newContentHeight = computedValues.m_extent - block->borderAndPaddingLogicalHeight() - block->scrollbarLogicalHeight();
-                LayoutUnit newHeight = block->adjustContentBoxLogicalHeightForBoxSizing(newContentHeight);
+            if (container->isOutOfFlowPositioned()
+                && container->style().height().isAuto()
+                && !(container->style().top().isAuto() || container->style().bottom().isAuto())) {
+                ASSERT_WITH_SECURITY_IMPLICATION(container->isRenderBlock());
+                auto& block = downcast<RenderBlock>(*container);
+                auto computedValues = block.computeLogicalHeight(block.logicalHeight(), 0);
+                LayoutUnit newContentHeight = computedValues.m_extent - block.borderAndPaddingLogicalHeight() - block.scrollbarLogicalHeight();
+                LayoutUnit newHeight = block.adjustContentBoxLogicalHeightForBoxSizing(newContentHeight);
                 return adjustContentBoxLogicalHeightForBoxSizing(valueForLength(logicalHeight, newHeight));
             }
             
@@ -2935,7 +3172,7 @@ LayoutUnit RenderBox::computeReplacedLogicalHeightUsing(Length logicalHeight) co
             // https://bugs.webkit.org/show_bug.cgi?id=46496
             LayoutUnit availableHeight;
             if (isOutOfFlowPositioned())
-                availableHeight = containingBlockLogicalHeightForPositioned(toRenderBoxModelObject(cb));
+                availableHeight = containingBlockLogicalHeightForPositioned(downcast<RenderBoxModelObject>(*container));
             else {
                 availableHeight = containingBlockLogicalHeightForContent(IncludeMarginBorderPadding);
                 // It is necessary to use the border-box to match WinIE's broken
@@ -2943,24 +3180,25 @@ LayoutUnit RenderBox::computeReplacedLogicalHeightUsing(Length logicalHeight) co
                 // table cells using percentage heights.
                 // FIXME: This needs to be made block-flow-aware.  If the cell and image are perpendicular block-flows, this isn't right.
                 // https://bugs.webkit.org/show_bug.cgi?id=46997
-                while (cb && !cb->isRenderView() && (cb->style().logicalHeight().isAuto() || cb->style().logicalHeight().isPercent())) {
-                    if (cb->isTableCell()) {
+                while (container && !is<RenderView>(*container)
+                    && (container->style().logicalHeight().isAuto() || container->style().logicalHeight().isPercentOrCalculated())) {
+                    if (container->isTableCell()) {
                         // Don't let table cells squeeze percent-height replaced elements
                         // <http://bugs.webkit.org/show_bug.cgi?id=15359>
                         availableHeight = std::max(availableHeight, intrinsicLogicalHeight());
                         return valueForLength(logicalHeight, availableHeight - borderAndPaddingLogicalHeight());
                     }
-                    toRenderBlock(cb)->addPercentHeightDescendant(const_cast<RenderBox&>(*this));
-                    cb = cb->containingBlock();
+                    downcast<RenderBlock>(*container).addPercentHeightDescendant(const_cast<RenderBox&>(*this));
+                    container = container->containingBlock();
                 }
             }
             return adjustContentBoxLogicalHeightForBoxSizing(valueForLength(logicalHeight, availableHeight));
         }
-        case ViewportPercentageWidth:
-        case ViewportPercentageHeight:
-        case ViewportPercentageMin:
-        case ViewportPercentageMax:
-            return adjustContentBoxLogicalHeightForBoxSizing(valueForLength(logicalHeight, 0));
+        case MinContent:
+        case MaxContent:
+        case FitContent:
+        case FillAvailable:
+            return adjustContentBoxLogicalHeightForBoxSizing(computeIntrinsicLogicalContentHeightUsing(logicalHeight, intrinsicLogicalHeight(), borderAndPaddingLogicalHeight()));
         default:
             return intrinsicLogicalHeight();
     }
@@ -2968,7 +3206,7 @@ LayoutUnit RenderBox::computeReplacedLogicalHeightUsing(Length logicalHeight) co
 
 LayoutUnit RenderBox::availableLogicalHeight(AvailableLogicalHeightType heightType) const
 {
-    return constrainLogicalHeightByMinMax(availableLogicalHeightUsing(style().logicalHeight(), heightType));
+    return constrainLogicalHeightByMinMax(availableLogicalHeightUsing(style().logicalHeight(), heightType), std::nullopt);
 }
 
 LayoutUnit RenderBox::availableLogicalHeightUsing(const Length& h, AvailableLogicalHeightType heightType) const
@@ -2976,29 +3214,27 @@ LayoutUnit RenderBox::availableLogicalHeightUsing(const Length& h, AvailableLogi
     // We need to stop here, since we don't want to increase the height of the table
     // artificially.  We're going to rely on this cell getting expanded to some new
     // height, and then when we lay out again we'll use the calculation below.
-    if (isTableCell() && (h.isAuto() || h.isPercent())) {
-        if (hasOverrideHeight())
+    if (isTableCell() && (h.isAuto() || h.isPercentOrCalculated())) {
+        if (hasOverrideLogicalContentHeight())
             return overrideLogicalContentHeight();
         return logicalHeight() - borderAndPaddingLogicalHeight();
     }
 
-    if (h.isPercent() && isOutOfFlowPositioned() && !isRenderFlowThread()) {
+    if (h.isPercentOrCalculated() && isOutOfFlowPositioned() && !isRenderFlowThread()) {
         // FIXME: This is wrong if the containingBlock has a perpendicular writing mode.
-        LayoutUnit availableHeight = containingBlockLogicalHeightForPositioned(containingBlock());
+        LayoutUnit availableHeight = containingBlockLogicalHeightForPositioned(*containingBlock());
         return adjustContentBoxLogicalHeightForBoxSizing(valueForLength(h, availableHeight));
     }
 
-    LayoutUnit heightIncludingScrollbar = computeContentAndScrollbarLogicalHeightUsing(h);
-    if (heightIncludingScrollbar != -1)
+    if (std::optional<LayoutUnit> heightIncludingScrollbar = computeContentAndScrollbarLogicalHeightUsing(MainOrPreferredSize, h, std::nullopt))
         return std::max<LayoutUnit>(0, adjustContentBoxLogicalHeightForBoxSizing(heightIncludingScrollbar) - scrollbarLogicalHeight());
 
     // FIXME: Check logicalTop/logicalBottom here to correctly handle vertical writing-mode.
     // https://bugs.webkit.org/show_bug.cgi?id=46500
-    if (isRenderBlock() && isOutOfFlowPositioned() && style().height().isAuto() && !(style().top().isAuto() || style().bottom().isAuto())) {
-        RenderBlock* block = const_cast<RenderBlock*>(toRenderBlock(this));
-        LogicalExtentComputedValues computedValues;
-        block->computeLogicalHeight(block->logicalHeight(), 0, computedValues);
-        LayoutUnit newContentHeight = computedValues.m_extent - block->borderAndPaddingLogicalHeight() - block->scrollbarLogicalHeight();
+    if (is<RenderBlock>(*this) && isOutOfFlowPositioned() && style().height().isAuto() && !(style().top().isAuto() || style().bottom().isAuto())) {
+        RenderBlock& block = const_cast<RenderBlock&>(downcast<RenderBlock>(*this));
+        auto computedValues = block.computeLogicalHeight(block.logicalHeight(), 0);
+        LayoutUnit newContentHeight = computedValues.m_extent - block.borderAndPaddingLogicalHeight() - block.scrollbarLogicalHeight();
         return adjustContentBoxLogicalHeightForBoxSizing(newContentHeight);
     }
 
@@ -3011,7 +3247,7 @@ LayoutUnit RenderBox::availableLogicalHeightUsing(const Length& h, AvailableLogi
     return availableHeight;
 }
 
-void RenderBox::computeBlockDirectionMargins(const RenderBlock* containingBlock, LayoutUnit& marginBefore, LayoutUnit& marginAfter) const
+void RenderBox::computeBlockDirectionMargins(const RenderBlock& containingBlock, LayoutUnit& marginBefore, LayoutUnit& marginAfter) const
 {
     if (isTableCell()) {
         // FIXME: Not right if we allow cells to have different directionality than the table.  If we do allow this, though,
@@ -3024,62 +3260,70 @@ void RenderBox::computeBlockDirectionMargins(const RenderBlock* containingBlock,
     // Margins are calculated with respect to the logical width of
     // the containing block (8.3)
     LayoutUnit cw = containingBlockLogicalWidthForContent();
-    const RenderStyle& containingBlockStyle = containingBlock->style();
+    const RenderStyle& containingBlockStyle = containingBlock.style();
     marginBefore = minimumValueForLength(style().marginBeforeUsing(&containingBlockStyle), cw);
     marginAfter = minimumValueForLength(style().marginAfterUsing(&containingBlockStyle), cw);
 }
 
-void RenderBox::computeAndSetBlockDirectionMargins(const RenderBlock* containingBlock)
+void RenderBox::computeAndSetBlockDirectionMargins(const RenderBlock& containingBlock)
 {
     LayoutUnit marginBefore;
     LayoutUnit marginAfter;
     computeBlockDirectionMargins(containingBlock, marginBefore, marginAfter);
-    containingBlock->setMarginBeforeForChild(*this, marginBefore);
-    containingBlock->setMarginAfterForChild(*this, marginAfter);
+    containingBlock.setMarginBeforeForChild(*this, marginBefore);
+    containingBlock.setMarginAfterForChild(*this, marginAfter);
 }
 
-LayoutUnit RenderBox::containingBlockLogicalWidthForPositioned(const RenderBoxModelObject* containingBlock, RenderRegion* region, bool checkForPerpendicularWritingMode) const
+LayoutUnit RenderBox::containingBlockLogicalWidthForPositioned(const RenderBoxModelObject& containingBlock, RenderRegion* region, bool checkForPerpendicularWritingMode) const
 {
-    if (checkForPerpendicularWritingMode && containingBlock->isHorizontalWritingMode() != isHorizontalWritingMode())
+    if (checkForPerpendicularWritingMode && containingBlock.isHorizontalWritingMode() != isHorizontalWritingMode())
         return containingBlockLogicalHeightForPositioned(containingBlock, false);
 
-    if (containingBlock->isBox()) {
+    if (hasOverrideContainingBlockLogicalWidth()) {
+        if (auto overrideLogicalWidth = overrideContainingBlockContentLogicalWidth())
+            return overrideLogicalWidth.value();
+    }
+
+    if (is<RenderBox>(containingBlock)) {
         bool isFixedPosition = style().position() == FixedPosition;
 
         RenderFlowThread* flowThread = flowThreadContainingBlock();
         if (!flowThread) {
-            if (isFixedPosition && containingBlock->isRenderView())
-                return toRenderView(containingBlock)->clientLogicalWidthForFixedPosition();
+            if (isFixedPosition && is<RenderView>(containingBlock))
+                return downcast<RenderView>(containingBlock).clientLogicalWidthForFixedPosition();
 
-            return toRenderBox(containingBlock)->clientLogicalWidth();
+            return downcast<RenderBox>(containingBlock).clientLogicalWidth();
         }
 
-        if (isFixedPosition && containingBlock->isRenderNamedFlowThread())
-            return containingBlock->view().clientLogicalWidth();
+        if (isFixedPosition && is<RenderNamedFlowThread>(containingBlock))
+            return containingBlock.view().clientLogicalWidth();
+
+        if (!is<RenderBlock>(containingBlock))
+            return downcast<RenderBox>(containingBlock).clientLogicalWidth();
 
-        const RenderBlock* cb = toRenderBlock(containingBlock);
-        RenderBoxRegionInfo* boxInfo = 0;
+        const RenderBlock& cb = downcast<RenderBlock>(containingBlock);
+        RenderBoxRegionInfo* boxInfo = nullptr;
         if (!region) {
-            if (containingBlock->isRenderFlowThread() && !checkForPerpendicularWritingMode)
-                return toRenderFlowThread(containingBlock)->contentLogicalWidthOfFirstRegion();
+            if (is<RenderFlowThread>(containingBlock) && !checkForPerpendicularWritingMode)
+                return downcast<RenderFlowThread>(containingBlock).contentLogicalWidthOfFirstRegion();
             if (isWritingModeRoot()) {
-                LayoutUnit cbPageOffset = cb->offsetFromLogicalTopOfFirstPage();
-                RenderRegion* cbRegion = cb->regionAtBlockOffset(cbPageOffset);
+                LayoutUnit cbPageOffset = cb.offsetFromLogicalTopOfFirstPage();
+                RenderRegion* cbRegion = cb.regionAtBlockOffset(cbPageOffset);
                 if (cbRegion)
-                    boxInfo = cb->renderBoxRegionInfo(cbRegion);
+                    boxInfo = cb.renderBoxRegionInfo(cbRegion);
             }
-        } else if (region && flowThread->isHorizontalWritingMode() == containingBlock->isHorizontalWritingMode()) {
-            RenderRegion* containingBlockRegion = cb->clampToStartAndEndRegions(region);
-            boxInfo = cb->renderBoxRegionInfo(containingBlockRegion);
+        } else if (flowThread->isHorizontalWritingMode() == containingBlock.isHorizontalWritingMode()) {
+            RenderRegion* containingBlockRegion = cb.clampToStartAndEndRegions(region);
+            boxInfo = cb.renderBoxRegionInfo(containingBlockRegion);
         }
-        return (boxInfo) ? std::max<LayoutUnit>(0, cb->clientLogicalWidth() - (cb->logicalWidth() - boxInfo->logicalWidth())) : cb->clientLogicalWidth();
+        return (boxInfo) ? std::max<LayoutUnit>(0, cb.clientLogicalWidth() - (cb.logicalWidth() - boxInfo->logicalWidth())) : cb.clientLogicalWidth();
     }
 
-    ASSERT(containingBlock->isRenderInline() && containingBlock->isInFlowPositioned());
+    ASSERT(containingBlock.isInFlowPositioned());
 
-    const RenderInline* flow = toRenderInline(containingBlock);
-    InlineFlowBox* first = flow->firstLineBox();
-    InlineFlowBox* last = flow->lastLineBox();
+    const auto& flow = downcast<RenderInline>(containingBlock);
+    InlineFlowBox* first = flow.firstLineBox();
+    InlineFlowBox* last = flow.lastLineBox();
 
     // If the containing block is empty, return a width of 0.
     if (!first || !last)
@@ -3087,7 +3331,7 @@ LayoutUnit RenderBox::containingBlockLogicalWidthForPositioned(const RenderBoxMo
 
     LayoutUnit fromLeft;
     LayoutUnit fromRight;
-    if (containingBlock->style().isLeftToRightDirection()) {
+    if (containingBlock.style().isLeftToRightDirection()) {
         fromLeft = first->logicalLeft() + first->borderLogicalLeft();
         fromRight = last->logicalLeft() + last->logicalWidth() - last->borderLogicalRight();
     } else {
@@ -3098,91 +3342,108 @@ LayoutUnit RenderBox::containingBlockLogicalWidthForPositioned(const RenderBoxMo
     return std::max<LayoutUnit>(0, fromRight - fromLeft);
 }
 
-LayoutUnit RenderBox::containingBlockLogicalHeightForPositioned(const RenderBoxModelObject* containingBlock, bool checkForPerpendicularWritingMode) const
+LayoutUnit RenderBox::containingBlockLogicalHeightForPositioned(const RenderBoxModelObject& containingBlock, bool checkForPerpendicularWritingMode) const
 {
-    if (checkForPerpendicularWritingMode && containingBlock->isHorizontalWritingMode() != isHorizontalWritingMode())
-        return containingBlockLogicalWidthForPositioned(containingBlock, 0, false);
+    if (checkForPerpendicularWritingMode && containingBlock.isHorizontalWritingMode() != isHorizontalWritingMode())
+        return containingBlockLogicalWidthForPositioned(containingBlock, nullptr, false);
+
+    if (hasOverrideContainingBlockLogicalHeight()) {
+        if (auto overrideLogicalHeight = overrideContainingBlockContentLogicalHeight())
+            return overrideLogicalHeight.value();
+    }
 
-    if (containingBlock->isBox()) {
+    if (containingBlock.isBox()) {
         bool isFixedPosition = style().position() == FixedPosition;
 
-        if (isFixedPosition && containingBlock->isRenderView())
-            return toRenderView(containingBlock)->clientLogicalHeightForFixedPosition();
+        if (isFixedPosition && is<RenderView>(containingBlock))
+            return downcast<RenderView>(containingBlock).clientLogicalHeightForFixedPosition();
 
-        const RenderBlock* cb = containingBlock->isRenderBlock() ? toRenderBlock(containingBlock) : containingBlock->containingBlock();
-        LayoutUnit result = cb->clientLogicalHeight();
+        const RenderBlock& cb = is<RenderBlock>(containingBlock) ? downcast<RenderBlock>(containingBlock) : *containingBlock.containingBlock();
+        LayoutUnit result = cb.clientLogicalHeight();
         RenderFlowThread* flowThread = flowThreadContainingBlock();
-        if (flowThread && containingBlock->isRenderFlowThread() && flowThread->isHorizontalWritingMode() == containingBlock->isHorizontalWritingMode()) {
-            if (containingBlock->isRenderNamedFlowThread() && isFixedPosition)
-                return containingBlock->view().clientLogicalHeight();
-            return toRenderFlowThread(containingBlock)->contentLogicalHeightOfFirstRegion();
+        if (flowThread && is<RenderFlowThread>(containingBlock) && flowThread->isHorizontalWritingMode() == containingBlock.isHorizontalWritingMode()) {
+            if (is<RenderNamedFlowThread>(containingBlock) && isFixedPosition)
+                return containingBlock.view().clientLogicalHeight();
+            return downcast<RenderFlowThread>(containingBlock).contentLogicalHeightOfFirstRegion();
         }
         return result;
     }
         
-    ASSERT(containingBlock->isRenderInline() && containingBlock->isInFlowPositioned());
+    ASSERT(containingBlock.isInFlowPositioned());
 
-    const RenderInline* flow = toRenderInline(containingBlock);
-    InlineFlowBox* first = flow->firstLineBox();
-    InlineFlowBox* last = flow->lastLineBox();
+    const auto& flow = downcast<RenderInline>(containingBlock);
+    InlineFlowBox* first = flow.firstLineBox();
+    InlineFlowBox* last = flow.lastLineBox();
 
     // If the containing block is empty, return a height of 0.
     if (!first || !last)
         return 0;
 
     LayoutUnit heightResult;
-    LayoutRect boundingBox = flow->linesBoundingBox();
-    if (containingBlock->isHorizontalWritingMode())
+    LayoutRect boundingBox = flow.linesBoundingBox();
+    if (containingBlock.isHorizontalWritingMode())
         heightResult = boundingBox.height();
     else
         heightResult = boundingBox.width();
-    heightResult -= (containingBlock->borderBefore() + containingBlock->borderAfter());
+    heightResult -= (containingBlock.borderBefore() + containingBlock.borderAfter());
     return heightResult;
 }
 
-static void computeInlineStaticDistance(Length& logicalLeft, Length& logicalRight, const RenderBox* child, const RenderBoxModelObject* containerBlock, LayoutUnit containerLogicalWidth, RenderRegion* region)
+static void computeInlineStaticDistance(Length& logicalLeft, Length& logicalRight, const RenderBox* child, const RenderBoxModelObject& containerBlock, LayoutUnit containerLogicalWidth, RenderRegion* region)
 {
     if (!logicalLeft.isAuto() || !logicalRight.isAuto())
         return;
 
     // FIXME: The static distance computation has not been patched for mixed writing modes yet.
     if (child->parent()->style().direction() == LTR) {
-        LayoutUnit staticPosition = child->layer()->staticInlinePosition() - containerBlock->borderLogicalLeft();
-        for (auto curr = child->parent(); curr && curr != containerBlock; curr = curr->container()) {
-            if (curr->isBox()) {
-                staticPosition += toRenderBox(curr)->logicalLeft();
-                if (region && toRenderBox(curr)->isRenderBlock()) {
-                    const RenderBlock* cb = toRenderBlock(curr);
-                    region = cb->clampToStartAndEndRegions(region);
-                    RenderBoxRegionInfo* boxInfo = cb->renderBoxRegionInfo(region);
-                    if (boxInfo)
-                        staticPosition += boxInfo->logicalLeft();
-                }
+        LayoutUnit staticPosition = child->layer()->staticInlinePosition() - containerBlock.borderLogicalLeft();
+        for (auto* current = child->parent(); current && current != &containerBlock; current = current->container()) {
+            if (!is<RenderBox>(*current))
+                continue;
+            const auto& renderBox = downcast<RenderBox>(*current);
+            staticPosition += renderBox.logicalLeft();
+            if (renderBox.isInFlowPositioned())
+                staticPosition += renderBox.isHorizontalWritingMode() ? renderBox.offsetForInFlowPosition().width() : renderBox.offsetForInFlowPosition().height();
+            if (region && is<RenderBlock>(*current)) {
+                const RenderBlock& currentBlock = downcast<RenderBlock>(*current);
+                region = currentBlock.clampToStartAndEndRegions(region);
+                RenderBoxRegionInfo* boxInfo = currentBlock.renderBoxRegionInfo(region);
+                if (boxInfo)
+                    staticPosition += boxInfo->logicalLeft();
             }
         }
         logicalLeft.setValue(Fixed, staticPosition);
     } else {
-        RenderBox* enclosingBox = child->parent()->enclosingBox();
-        LayoutUnit staticPosition = child->layer()->staticInlinePosition() + containerLogicalWidth + containerBlock->borderLogicalLeft();
-        for (RenderElement* curr = enclosingBox; curr; curr = curr->container()) {
-            if (curr->isBox()) {
-                if (curr != containerBlock)
-                    staticPosition -= toRenderBox(curr)->logicalLeft();
-                if (curr == enclosingBox)
-                    staticPosition -= enclosingBox->logicalWidth();
-                if (region && curr->isRenderBlock()) {
-                    const RenderBlock* cb = toRenderBlock(curr);
-                    region = cb->clampToStartAndEndRegions(region);
-                    RenderBoxRegionInfo* boxInfo = cb->renderBoxRegionInfo(region);
-                    if (boxInfo) {
-                        if (curr != containerBlock)
-                            staticPosition -= cb->logicalWidth() - (boxInfo->logicalLeft() + boxInfo->logicalWidth());
-                        if (curr == enclosingBox)
-                            staticPosition += enclosingBox->logicalWidth() - boxInfo->logicalWidth();
-                    }
+        LayoutUnit staticPosition = child->layer()->staticInlinePosition() + containerLogicalWidth + containerBlock.borderLogicalLeft();
+        auto& enclosingBox = child->parent()->enclosingBox();
+        if (&enclosingBox != &containerBlock && containerBlock.isDescendantOf(&enclosingBox)) {
+            logicalRight.setValue(Fixed, staticPosition);
+            return;
+        }
+
+        staticPosition -= enclosingBox.logicalWidth();
+        for (const RenderElement* current = &enclosingBox; current; current = current->container()) {
+            if (!is<RenderBox>(*current))
+                continue;
+
+            if (current != &containerBlock) {
+                auto& renderBox = downcast<RenderBox>(*current);
+                staticPosition -= renderBox.logicalLeft();
+                if (renderBox.isInFlowPositioned())
+                    staticPosition -= renderBox.isHorizontalWritingMode() ? renderBox.offsetForInFlowPosition().width() : renderBox.offsetForInFlowPosition().height();
+            }
+            if (region && is<RenderBlock>(*current)) {
+                auto& currentBlock = downcast<RenderBlock>(*current);
+                region = currentBlock.clampToStartAndEndRegions(region);
+                RenderBoxRegionInfo* boxInfo = currentBlock.renderBoxRegionInfo(region);
+                if (boxInfo) {
+                    if (current != &containerBlock)
+                        staticPosition -= currentBlock.logicalWidth() - (boxInfo->logicalLeft() + boxInfo->logicalWidth());
+                    if (current == &enclosingBox)
+                        staticPosition += enclosingBox.logicalWidth() - boxInfo->logicalWidth();
                 }
             }
-            if (curr == containerBlock)
+            if (current == &containerBlock)
                 break;
         }
         logicalRight.setValue(Fixed, staticPosition);
@@ -3216,14 +3477,14 @@ void RenderBox::computePositionedLogicalWidth(LogicalExtentComputedValues& compu
 
     // We don't use containingBlock(), since we may be positioned by an enclosing
     // relative positioned inline.
-    const RenderBoxModelObject* containerBlock = toRenderBoxModelObject(container());
+    const RenderBoxModelObject& containerBlock = downcast<RenderBoxModelObject>(*container());
     
     const LayoutUnit containerLogicalWidth = containingBlockLogicalWidthForPositioned(containerBlock, region);
 
     // Use the container block's direction except when calculating the static distance
     // This conforms with the reference results for abspos-replaced-width-margin-000.htm
     // of the CSS 2.1 test suite
-    TextDirection containerDirection = containerBlock->style().direction();
+    TextDirection containerDirection = containerBlock.style().direction();
 
     bool isHorizontal = isHorizontalWritingMode();
     const LayoutUnit bordersPlusPadding = borderAndPaddingLogicalWidth();
@@ -3262,7 +3523,7 @@ void RenderBox::computePositionedLogicalWidth(LogicalExtentComputedValues& compu
     computeInlineStaticDistance(logicalLeftLength, logicalRightLength, this, containerBlock, containerLogicalWidth, region);
     
     // Calculate constraint equation values for 'width' case.
-    computePositionedLogicalWidthUsing(style().logicalWidth(), containerBlock, containerDirection,
+    computePositionedLogicalWidthUsing(MainOrPreferredSize, style().logicalWidth(), containerBlock, containerDirection,
                                        containerLogicalWidth, bordersPlusPadding,
                                        logicalLeftLength, logicalRightLength, marginLogicalLeft, marginLogicalRight,
                                        computedValues);
@@ -3271,7 +3532,7 @@ void RenderBox::computePositionedLogicalWidth(LogicalExtentComputedValues& compu
     if (!style().logicalMaxWidth().isUndefined()) {
         LogicalExtentComputedValues maxValues;
 
-        computePositionedLogicalWidthUsing(style().logicalMaxWidth(), containerBlock, containerDirection,
+        computePositionedLogicalWidthUsing(MaxSize, style().logicalMaxWidth(), containerBlock, containerDirection,
                                            containerLogicalWidth, bordersPlusPadding,
                                            logicalLeftLength, logicalRightLength, marginLogicalLeft, marginLogicalRight,
                                            maxValues);
@@ -3288,7 +3549,7 @@ void RenderBox::computePositionedLogicalWidth(LogicalExtentComputedValues& compu
     if (!style().logicalMinWidth().isZero() || style().logicalMinWidth().isIntrinsic()) {
         LogicalExtentComputedValues minValues;
 
-        computePositionedLogicalWidthUsing(style().logicalMinWidth(), containerBlock, containerDirection,
+        computePositionedLogicalWidthUsing(MinSize, style().logicalMinWidth(), containerBlock, containerDirection,
                                            containerLogicalWidth, bordersPlusPadding,
                                            logicalLeftLength, logicalRightLength, marginLogicalLeft, marginLogicalRight,
                                            minValues);
@@ -3301,19 +3562,27 @@ void RenderBox::computePositionedLogicalWidth(LogicalExtentComputedValues& compu
         }
     }
 
+    if (!style().hasStaticInlinePosition(isHorizontal))
+        computedValues.m_position += extraInlineOffset();
+
     computedValues.m_extent += bordersPlusPadding;
+    if (is<RenderBox>(containerBlock)) {
+        auto& containingBox = downcast<RenderBox>(containerBlock);
+        if (containingBox.shouldPlaceBlockDirectionScrollbarOnLeft())
+            computedValues.m_position += containingBox.verticalScrollbarWidth();
+    }
     
     // Adjust logicalLeft if we need to for the flipped version of our writing mode in regions.
     // FIXME: Add support for other types of objects as containerBlock, not only RenderBlock.
     RenderFlowThread* flowThread = flowThreadContainingBlock();
-    if (flowThread && !region && isWritingModeRoot() && isHorizontalWritingMode() == containerBlock->isHorizontalWritingMode() && containerBlock->isRenderBlock()) {
-        ASSERT(containerBlock->canHaveBoxInfoInRegion());
+    if (flowThread && !region && isWritingModeRoot() && isHorizontalWritingMode() == containerBlock.isHorizontalWritingMode() && is<RenderBlock>(containerBlock)) {
+        ASSERT(containerBlock.canHaveBoxInfoInRegion());
         LayoutUnit logicalLeftPos = computedValues.m_position;
-        const RenderBlock* cb = toRenderBlock(containerBlock);
-        LayoutUnit cbPageOffset = cb->offsetFromLogicalTopOfFirstPage();
-        RenderRegion* cbRegion = cb->regionAtBlockOffset(cbPageOffset);
+        const RenderBlock& renderBlock = downcast<RenderBlock>(containerBlock);
+        LayoutUnit cbPageOffset = renderBlock.offsetFromLogicalTopOfFirstPage();
+        RenderRegion* cbRegion = renderBlock.regionAtBlockOffset(cbPageOffset);
         if (cbRegion) {
-            RenderBoxRegionInfo* boxInfo = cb->renderBoxRegionInfo(cbRegion);
+            RenderBoxRegionInfo* boxInfo = renderBlock.renderBoxRegionInfo(cbRegion);
             if (boxInfo) {
                 logicalLeftPos += boxInfo->logicalLeft();
                 computedValues.m_position = logicalLeftPos;
@@ -3322,23 +3591,26 @@ void RenderBox::computePositionedLogicalWidth(LogicalExtentComputedValues& compu
     }
 }
 
-static void computeLogicalLeftPositionedOffset(LayoutUnit& logicalLeftPos, const RenderBox* child, LayoutUnit logicalWidthValue, const RenderBoxModelObject* containerBlock, LayoutUnit containerLogicalWidth)
+static void computeLogicalLeftPositionedOffset(LayoutUnit& logicalLeftPos, const RenderBox* child, LayoutUnit logicalWidthValue, const RenderBoxModelObject& containerBlock, LayoutUnit containerLogicalWidth)
 {
     // Deal with differing writing modes here.  Our offset needs to be in the containing block's coordinate space. If the containing block is flipped
     // along this axis, then we need to flip the coordinate.  This can only happen if the containing block is both a flipped mode and perpendicular to us.
-    if (containerBlock->isHorizontalWritingMode() != child->isHorizontalWritingMode() && containerBlock->style().isFlippedBlocksWritingMode()) {
+    if (containerBlock.isHorizontalWritingMode() != child->isHorizontalWritingMode() && containerBlock.style().isFlippedBlocksWritingMode()) {
         logicalLeftPos = containerLogicalWidth - logicalWidthValue - logicalLeftPos;
-        logicalLeftPos += (child->isHorizontalWritingMode() ? containerBlock->borderRight() : containerBlock->borderBottom());
+        logicalLeftPos += (child->isHorizontalWritingMode() ? containerBlock.borderRight() : containerBlock.borderBottom());
     } else
-        logicalLeftPos += (child->isHorizontalWritingMode() ? containerBlock->borderLeft() : containerBlock->borderTop());
+        logicalLeftPos += (child->isHorizontalWritingMode() ? containerBlock.borderLeft() : containerBlock.borderTop());
 }
 
-void RenderBox::computePositionedLogicalWidthUsing(Length logicalWidth, const RenderBoxModelObject* containerBlock, TextDirection containerDirection,
+void RenderBox::computePositionedLogicalWidthUsing(SizeType widthType, Length logicalWidth, const RenderBoxModelObject& containerBlock, TextDirection containerDirection,
                                                    LayoutUnit containerLogicalWidth, LayoutUnit bordersPlusPadding,
                                                    Length logicalLeft, Length logicalRight, Length marginLogicalLeft, Length marginLogicalRight,
                                                    LogicalExtentComputedValues& computedValues) const
 {
-    if (logicalWidth.isIntrinsic())
+    ASSERT(widthType == MinSize || widthType == MainOrPreferredSize || !logicalWidth.isAuto());
+    if (widthType == MinSize && logicalWidth.isAuto())
+        logicalWidth = Length(0, Fixed);
+    else if (logicalWidth.isIntrinsic())
         logicalWidth = Length(computeIntrinsicLogicalWidthUsing(logicalWidth, containerLogicalWidth, bordersPlusPadding) - bordersPlusPadding, Fixed);
 
     // 'left' and 'right' cannot both be 'auto' because one would of been
@@ -3347,7 +3619,7 @@ void RenderBox::computePositionedLogicalWidthUsing(Length logicalWidth, const Re
 
     LayoutUnit logicalLeftValue = 0;
 
-    const LayoutUnit containerRelativeLogicalWidth = containingBlockLogicalWidthForPositioned(containerBlock, 0, false);
+    const LayoutUnit containerRelativeLogicalWidth = containingBlockLogicalWidthForPositioned(containerBlock, nullptr, false);
 
     bool logicalWidthIsAuto = logicalWidth.isIntrinsicOrAuto();
     bool logicalLeftIsAuto = logicalLeft.isAuto();
@@ -3501,10 +3773,10 @@ void RenderBox::computePositionedLogicalWidthUsing(Length logicalWidth, const Re
     // positioned, inline because right now, it is using the logical left position
     // of the first line box when really it should use the last line box.  When
     // this is fixed elsewhere, this block should be removed.
-    if (containerBlock->isRenderInline() && !containerBlock->style().isLeftToRightDirection()) {
-        const RenderInline* flow = toRenderInline(containerBlock);
-        InlineFlowBox* firstLine = flow->firstLineBox();
-        InlineFlowBox* lastLine = flow->lastLineBox();
+    if (is<RenderInline>(containerBlock) && !containerBlock.style().isLeftToRightDirection()) {
+        const auto& flow = downcast<RenderInline>(containerBlock);
+        InlineFlowBox* firstLine = flow.firstLineBox();
+        InlineFlowBox* lastLine = flow.lastLineBox();
         if (firstLine && lastLine && firstLine != lastLine) {
             computedValues.m_position = logicalLeftValue + marginLogicalLeftValue + lastLine->borderLogicalLeft() + (lastLine->logicalLeft() - firstLine->logicalLeft());
             return;
@@ -3515,16 +3787,21 @@ void RenderBox::computePositionedLogicalWidthUsing(Length logicalWidth, const Re
     computeLogicalLeftPositionedOffset(computedValues.m_position, this, computedValues.m_extent, containerBlock, containerLogicalWidth);
 }
 
-static void computeBlockStaticDistance(Length& logicalTop, Length& logicalBottom, const RenderBox* child, const RenderBoxModelObject* containerBlock)
+static void computeBlockStaticDistance(Length& logicalTop, Length& logicalBottom, const RenderBox* child, const RenderBoxModelObject& containerBlock)
 {
     if (!logicalTop.isAuto() || !logicalBottom.isAuto())
         return;
     
     // FIXME: The static distance computation has not been patched for mixed writing modes.
-    LayoutUnit staticLogicalTop = child->layer()->staticBlockPosition() - containerBlock->borderBefore();
-    for (RenderElement* curr = child->parent(); curr && curr != containerBlock; curr = curr->container()) {
-        if (curr->isBox() && !curr->isTableRow())
-            staticLogicalTop += toRenderBox(curr)->logicalTop();
+    LayoutUnit staticLogicalTop = child->layer()->staticBlockPosition() - containerBlock.borderBefore();
+    for (RenderElement* container = child->parent(); container && container != &containerBlock; container = container->container()) {
+        if (!is<RenderBox>(*container))
+            continue;
+        const auto& renderBox = downcast<RenderBox>(*container);
+        if (!is<RenderTableRow>(renderBox))
+            staticLogicalTop += renderBox.logicalTop();
+        if (renderBox.isInFlowPositioned())
+            staticLogicalTop += renderBox.isHorizontalWritingMode() ? renderBox.offsetForInFlowPosition().height() : renderBox.offsetForInFlowPosition().width();
     }
     logicalTop.setValue(Fixed, staticLogicalTop);
 }
@@ -3544,7 +3821,7 @@ void RenderBox::computePositionedLogicalHeight(LogicalExtentComputedValues& comp
 
 
     // We don't use containingBlock(), since we may be positioned by an enclosing relpositioned inline.
-    const RenderBoxModelObject* containerBlock = toRenderBoxModelObject(container());
+    const RenderBoxModelObject& containerBlock = downcast<RenderBoxModelObject>(*container());
 
     const LayoutUnit containerLogicalHeight = containingBlockLogicalHeightForPositioned(containerBlock);
 
@@ -3578,7 +3855,7 @@ void RenderBox::computePositionedLogicalHeight(LogicalExtentComputedValues& comp
 
     // Calculate constraint equation values for 'height' case.
     LayoutUnit logicalHeight = computedValues.m_extent;
-    computePositionedLogicalHeightUsing(styleToUse.logicalHeight(), containerBlock, containerLogicalHeight, bordersPlusPadding, logicalHeight,
+    computePositionedLogicalHeightUsing(MainOrPreferredSize, styleToUse.logicalHeight(), containerBlock, containerLogicalHeight, bordersPlusPadding, logicalHeight,
                                         logicalTopLength, logicalBottomLength, marginBefore, marginAfter,
                                         computedValues);
 
@@ -3589,7 +3866,7 @@ void RenderBox::computePositionedLogicalHeight(LogicalExtentComputedValues& comp
     if (!styleToUse.logicalMaxHeight().isUndefined()) {
         LogicalExtentComputedValues maxValues;
 
-        computePositionedLogicalHeightUsing(styleToUse.logicalMaxHeight(), containerBlock, containerLogicalHeight, bordersPlusPadding, logicalHeight,
+        computePositionedLogicalHeightUsing(MaxSize, styleToUse.logicalMaxHeight(), containerBlock, containerLogicalHeight, bordersPlusPadding, logicalHeight,
                                             logicalTopLength, logicalBottomLength, marginBefore, marginAfter,
                                             maxValues);
 
@@ -3602,10 +3879,10 @@ void RenderBox::computePositionedLogicalHeight(LogicalExtentComputedValues& comp
     }
 
     // Calculate constraint equation values for 'min-height' case.
-    if (!styleToUse.logicalMinHeight().isZero()) {
+    if (!styleToUse.logicalMinHeight().isZero() || styleToUse.logicalMinHeight().isIntrinsic()) {
         LogicalExtentComputedValues minValues;
 
-        computePositionedLogicalHeightUsing(styleToUse.logicalMinHeight(), containerBlock, containerLogicalHeight, bordersPlusPadding, logicalHeight,
+        computePositionedLogicalHeightUsing(MinSize, styleToUse.logicalMinHeight(), containerBlock, containerLogicalHeight, bordersPlusPadding, logicalHeight,
                                             logicalTopLength, logicalBottomLength, marginBefore, marginAfter,
                                             minValues);
 
@@ -3617,20 +3894,23 @@ void RenderBox::computePositionedLogicalHeight(LogicalExtentComputedValues& comp
         }
     }
 
+    if (!style().hasStaticBlockPosition(isHorizontalWritingMode()))
+        computedValues.m_position += extraBlockOffset();
+
     // Set final height value.
     computedValues.m_extent += bordersPlusPadding;
     
     // Adjust logicalTop if we need to for perpendicular writing modes in regions.
     // FIXME: Add support for other types of objects as containerBlock, not only RenderBlock.
     RenderFlowThread* flowThread = flowThreadContainingBlock();
-    if (flowThread && isHorizontalWritingMode() != containerBlock->isHorizontalWritingMode() && containerBlock->isRenderBlock()) {
-        ASSERT(containerBlock->canHaveBoxInfoInRegion());
+    if (flowThread && isHorizontalWritingMode() != containerBlock.isHorizontalWritingMode() && is<RenderBlock>(containerBlock)) {
+        ASSERT(containerBlock.canHaveBoxInfoInRegion());
         LayoutUnit logicalTopPos = computedValues.m_position;
-        const RenderBlock* cb = toRenderBlock(containerBlock);
-        LayoutUnit cbPageOffset = cb->offsetFromLogicalTopOfFirstPage() - logicalLeft();
-        RenderRegion* cbRegion = cb->regionAtBlockOffset(cbPageOffset);
+        const RenderBlock& renderBox = downcast<RenderBlock>(containerBlock);
+        LayoutUnit cbPageOffset = renderBox.offsetFromLogicalTopOfFirstPage() - logicalLeft();
+        RenderRegion* cbRegion = renderBox.regionAtBlockOffset(cbPageOffset);
         if (cbRegion) {
-            RenderBoxRegionInfo* boxInfo = cb->renderBoxRegionInfo(cbRegion);
+            RenderBoxRegionInfo* boxInfo = renderBox.renderBoxRegionInfo(cbRegion);
             if (boxInfo) {
                 logicalTopPos += boxInfo->logicalLeft();
                 computedValues.m_position = logicalTopPos;
@@ -3639,33 +3919,37 @@ void RenderBox::computePositionedLogicalHeight(LogicalExtentComputedValues& comp
     }
 }
 
-static void computeLogicalTopPositionedOffset(LayoutUnit& logicalTopPos, const RenderBox* child, LayoutUnit logicalHeightValue, const RenderBoxModelObject* containerBlock, LayoutUnit containerLogicalHeight)
+static void computeLogicalTopPositionedOffset(LayoutUnit& logicalTopPos, const RenderBox* child, LayoutUnit logicalHeightValue, const RenderBoxModelObject& containerBlock, LayoutUnit containerLogicalHeight)
 {
     // Deal with differing writing modes here.  Our offset needs to be in the containing block's coordinate space. If the containing block is flipped
     // along this axis, then we need to flip the coordinate.  This can only happen if the containing block is both a flipped mode and perpendicular to us.
-    if ((child->style().isFlippedBlocksWritingMode() && child->isHorizontalWritingMode() != containerBlock->isHorizontalWritingMode())
-        || (child->style().isFlippedBlocksWritingMode() != containerBlock->style().isFlippedBlocksWritingMode() && child->isHorizontalWritingMode() == containerBlock->isHorizontalWritingMode()))
+    if ((child->style().isFlippedBlocksWritingMode() && child->isHorizontalWritingMode() != containerBlock.isHorizontalWritingMode())
+        || (child->style().isFlippedBlocksWritingMode() != containerBlock.style().isFlippedBlocksWritingMode() && child->isHorizontalWritingMode() == containerBlock.isHorizontalWritingMode()))
         logicalTopPos = containerLogicalHeight - logicalHeightValue - logicalTopPos;
 
     // Our offset is from the logical bottom edge in a flipped environment, e.g., right for vertical-rl and bottom for horizontal-bt.
-    if (containerBlock->style().isFlippedBlocksWritingMode() && child->isHorizontalWritingMode() == containerBlock->isHorizontalWritingMode()) {
+    if (containerBlock.style().isFlippedBlocksWritingMode() && child->isHorizontalWritingMode() == containerBlock.isHorizontalWritingMode()) {
         if (child->isHorizontalWritingMode())
-            logicalTopPos += containerBlock->borderBottom();
+            logicalTopPos += containerBlock.borderBottom();
         else
-            logicalTopPos += containerBlock->borderRight();
+            logicalTopPos += containerBlock.borderRight();
     } else {
         if (child->isHorizontalWritingMode())
-            logicalTopPos += containerBlock->borderTop();
+            logicalTopPos += containerBlock.borderTop();
         else
-            logicalTopPos += containerBlock->borderLeft();
+            logicalTopPos += containerBlock.borderLeft();
     }
 }
 
-void RenderBox::computePositionedLogicalHeightUsing(Length logicalHeightLength, const RenderBoxModelObject* containerBlock,
+void RenderBox::computePositionedLogicalHeightUsing(SizeType heightType, Length logicalHeightLength, const RenderBoxModelObject& containerBlock,
                                                     LayoutUnit containerLogicalHeight, LayoutUnit bordersPlusPadding, LayoutUnit logicalHeight,
                                                     Length logicalTop, Length logicalBottom, Length marginBefore, Length marginAfter,
                                                     LogicalExtentComputedValues& computedValues) const
 {
+    ASSERT(heightType == MinSize || heightType == MainOrPreferredSize || !logicalHeightLength.isAuto());
+    if (heightType == MinSize && logicalHeightLength.isAuto())
+        logicalHeightLength = Length(0, Fixed);
+
     // 'top' and 'bottom' cannot both be 'auto' because 'top would of been
     // converted to the static position in computePositionedLogicalHeight()
     ASSERT(!(logicalTop.isAuto() && logicalBottom.isAuto()));
@@ -3673,7 +3957,7 @@ void RenderBox::computePositionedLogicalHeightUsing(Length logicalHeightLength,
     LayoutUnit logicalHeightValue;
     LayoutUnit contentLogicalHeight = logicalHeight - bordersPlusPadding;
 
-    const LayoutUnit containerRelativeLogicalWidth = containingBlockLogicalWidthForPositioned(containerBlock, 0, false);
+    const LayoutUnit containerRelativeLogicalWidth = containingBlockLogicalWidthForPositioned(containerBlock, nullptr, false);
 
     LayoutUnit logicalTopValue = 0;
 
@@ -3682,9 +3966,15 @@ void RenderBox::computePositionedLogicalHeightUsing(Length logicalHeightLength,
     bool logicalBottomIsAuto = logicalBottom.isAuto();
 
     // Height is never unsolved for tables.
+    LayoutUnit resolvedLogicalHeight;
     if (isTable()) {
-        logicalHeightLength.setValue(Fixed, contentLogicalHeight);
+        resolvedLogicalHeight = contentLogicalHeight;
         logicalHeightIsAuto = false;
+    } else {
+        if (logicalHeightLength.isIntrinsic())
+            resolvedLogicalHeight = computeIntrinsicLogicalContentHeightUsing(logicalHeightLength, contentLogicalHeight, bordersPlusPadding).value();
+        else
+            resolvedLogicalHeight = adjustContentBoxLogicalHeightForBoxSizing(valueForLength(logicalHeightLength, containerLogicalHeight));
     }
 
     if (!logicalTopIsAuto && !logicalHeightIsAuto && !logicalBottomIsAuto) {
@@ -3699,7 +3989,7 @@ void RenderBox::computePositionedLogicalHeightUsing(Length logicalHeightLength,
         // NOTE:  It is not necessary to solve for 'bottom' in the over constrained
         // case because the value is not used for any further calculations.
 
-        logicalHeightValue = adjustContentBoxLogicalHeightForBoxSizing(valueForLength(logicalHeightLength, containerLogicalHeight));
+        logicalHeightValue = resolvedLogicalHeight;
         logicalTopValue = valueForLength(logicalTop, containerLogicalHeight);
 
         const LayoutUnit availableSpace = containerLogicalHeight - (logicalTopValue + logicalHeightValue + valueForLength(logicalBottom, containerLogicalHeight) + bordersPlusPadding);
@@ -3766,7 +4056,7 @@ void RenderBox::computePositionedLogicalHeightUsing(Length logicalHeightLength,
             logicalHeightValue = contentLogicalHeight;
         } else if (logicalTopIsAuto && !logicalHeightIsAuto && !logicalBottomIsAuto) {
             // RULE 4: (solve of top)
-            logicalHeightValue = adjustContentBoxLogicalHeightForBoxSizing(valueForLength(logicalHeightLength, containerLogicalHeight));
+            logicalHeightValue = resolvedLogicalHeight;
             logicalTopValue = availableSpace - (logicalHeightValue + valueForLength(logicalBottom, containerLogicalHeight));
         } else if (!logicalTopIsAuto && logicalHeightIsAuto && !logicalBottomIsAuto) {
             // RULE 5: (solve of height)
@@ -3774,7 +4064,7 @@ void RenderBox::computePositionedLogicalHeightUsing(Length logicalHeightLength,
             logicalHeightValue = std::max<LayoutUnit>(0, availableSpace - (logicalTopValue + valueForLength(logicalBottom, containerLogicalHeight)));
         } else if (!logicalTopIsAuto && !logicalHeightIsAuto && logicalBottomIsAuto) {
             // RULE 6: (no need solve of bottom)
-            logicalHeightValue = adjustContentBoxLogicalHeightForBoxSizing(valueForLength(logicalHeightLength, containerLogicalHeight));
+            logicalHeightValue = resolvedLogicalHeight;
             logicalTopValue = valueForLength(logicalTop, containerLogicalHeight);
         }
     }
@@ -3795,14 +4085,14 @@ void RenderBox::computePositionedLogicalWidthReplaced(LogicalExtentComputedValue
 
     // We don't use containingBlock(), since we may be positioned by an enclosing
     // relative positioned inline.
-    const RenderBoxModelObject* containerBlock = toRenderBoxModelObject(container());
+    const RenderBoxModelObject& containerBlock = downcast<RenderBoxModelObject>(*container());
 
     const LayoutUnit containerLogicalWidth = containingBlockLogicalWidthForPositioned(containerBlock);
-    const LayoutUnit containerRelativeLogicalWidth = containingBlockLogicalWidthForPositioned(containerBlock, 0, false);
+    const LayoutUnit containerRelativeLogicalWidth = containingBlockLogicalWidthForPositioned(containerBlock, nullptr, false);
 
     // To match WinIE, in quirks mode use the parent's 'direction' property
     // instead of the the container block's.
-    TextDirection containerDirection = containerBlock->style().direction();
+    TextDirection containerDirection = containerBlock.style().direction();
 
     // Variables to solve.
     bool isHorizontal = isHorizontalWritingMode();
@@ -3830,7 +4120,7 @@ void RenderBox::computePositionedLogicalWidthReplaced(LogicalExtentComputedValue
      *    else if 'direction' is 'rtl', set 'right' to the static position.
     \*-----------------------------------------------------------------------*/
     // see FIXME 1
-    computeInlineStaticDistance(logicalLeft, logicalRight, this, containerBlock, containerLogicalWidth, 0); // FIXME: Pass the region.
+    computeInlineStaticDistance(logicalLeft, logicalRight, this, containerBlock, containerLogicalWidth, nullptr); // FIXME: Pass the region.
 
     /*-----------------------------------------------------------------------*\
      * 3. If 'left' or 'right' are 'auto', replace any 'auto' on 'margin-left'
@@ -3939,10 +4229,10 @@ void RenderBox::computePositionedLogicalWidthReplaced(LogicalExtentComputedValue
     // positioned, inline containing block because right now, it is using the logical left position
     // of the first line box when really it should use the last line box.  When
     // this is fixed elsewhere, this block should be removed.
-    if (containerBlock->isRenderInline() && !containerBlock->style().isLeftToRightDirection()) {
-        const RenderInline* flow = toRenderInline(containerBlock);
-        InlineFlowBox* firstLine = flow->firstLineBox();
-        InlineFlowBox* lastLine = flow->lastLineBox();
+    if (is<RenderInline>(containerBlock) && !containerBlock.style().isLeftToRightDirection()) {
+        const auto& flow = downcast<RenderInline>(containerBlock);
+        InlineFlowBox* firstLine = flow.firstLineBox();
+        InlineFlowBox* lastLine = flow.lastLineBox();
         if (firstLine && lastLine && firstLine != lastLine) {
             computedValues.m_position = logicalLeftValue + marginLogicalLeftAlias + lastLine->borderLogicalLeft() + (lastLine->logicalLeft() - firstLine->logicalLeft());
             return;
@@ -3963,10 +4253,10 @@ void RenderBox::computePositionedLogicalHeightReplaced(LogicalExtentComputedValu
     // the numbers correspond to numbers in spec)
 
     // We don't use containingBlock(), since we may be positioned by an enclosing relpositioned inline.
-    const RenderBoxModelObject* containerBlock = toRenderBoxModelObject(container());
+    const RenderBoxModelObject& containerBlock = downcast<RenderBoxModelObject>(*container());
 
     const LayoutUnit containerLogicalHeight = containingBlockLogicalHeightForPositioned(containerBlock);
-    const LayoutUnit containerRelativeLogicalWidth = containingBlockLogicalWidthForPositioned(containerBlock, 0, false);
+    const LayoutUnit containerRelativeLogicalWidth = containingBlockLogicalWidthForPositioned(containerBlock, nullptr, false);
 
     // Variables to solve.
     Length marginBefore = style().marginBefore();
@@ -4083,7 +4373,7 @@ void RenderBox::computePositionedLogicalHeightReplaced(LogicalExtentComputedValu
     computedValues.m_position = logicalTopPos;
 }
 
-LayoutRect RenderBox::localCaretRect(InlineBox* box, int caretOffset, LayoutUnit* extraWidthToEndOfLine)
+LayoutRect RenderBox::localCaretRect(InlineBox* box, unsigned caretOffset, LayoutUnit* extraWidthToEndOfLine)
 {
     // VisiblePositions at offsets inside containers either a) refer to the positions before/after
     // those containers (tables and select elements) or b) refer to the position inside an empty block.
@@ -4124,7 +4414,7 @@ LayoutRect RenderBox::localCaretRect(InlineBox* box, int caretOffset, LayoutUnit
     // FIXME: Border/padding should be added for all elements but this workaround
     // is needed because we use offsets inside an "atomic" element to represent
     // positions before and after the element in deprecated editing offsets.
-    if (element() && !(editingIgnoresContent(element()) || isTableElement(element()))) {
+    if (element() && !(editingIgnoresContent(*element()) || isRenderedTable(element()))) {
         rect.setX(rect.x() + borderLeft() + paddingLeft());
         rect.setY(rect.y() + paddingTop() + borderTop());
     }
@@ -4135,15 +4425,15 @@ LayoutRect RenderBox::localCaretRect(InlineBox* box, int caretOffset, LayoutUnit
     return rect;
 }
 
-VisiblePosition RenderBox::positionForPoint(const LayoutPoint& point)
+VisiblePosition RenderBox::positionForPoint(const LayoutPoint& point, const RenderRegion* region)
 {
     // no children...return this render object's element, if there is one, and offset 0
     if (!firstChild())
         return createVisiblePosition(nonPseudoElement() ? firstPositionInOrBeforeNode(nonPseudoElement()) : Position());
 
     if (isTable() && nonPseudoElement()) {
-        LayoutUnit right = contentWidth() + borderAndPaddingWidth();
-        LayoutUnit bottom = contentHeight() + borderAndPaddingHeight();
+        LayoutUnit right = contentWidth() + horizontalBorderAndPaddingExtent();
+        LayoutUnit bottom = contentHeight() + verticalBorderAndPaddingExtent();
         
         if (point.x() < 0 || point.x() > right || point.y() < 0 || point.y() > bottom) {
             if (point.x() <= right / 2)
@@ -4154,29 +4444,31 @@ VisiblePosition RenderBox::positionForPoint(const LayoutPoint& point)
 
     // Pass off to the closest child.
     LayoutUnit minDist = LayoutUnit::max();
-    RenderBox* closestRenderer = 0;
+    RenderBox* closestRenderer = nullptr;
     LayoutPoint adjustedPoint = point;
     if (isTableRow())
         adjustedPoint.moveBy(location());
 
-    for (RenderObject* renderObject = firstChild(); renderObject; renderObject = renderObject->nextSibling()) {
-        if (!renderObject->isBox())
-            continue;
-        RenderBox* renderer = toRenderBox(renderObject);
+    for (auto& renderer : childrenOfType<RenderBox>(*this)) {
+        if (is<RenderFlowThread>(*this)) {
+            ASSERT(region);
+            if (!downcast<RenderFlowThread>(*this).objectShouldFragmentInFlowRegion(&renderer, region))
+                continue;
+        }
 
-        if ((!renderer->firstChild() && !renderer->isInline() && !renderer->isRenderBlockFlow() )
-            || renderer->style().visibility() != VISIBLE)
+        if ((!renderer.firstChild() && !renderer.isInline() && !is<RenderBlockFlow>(renderer))
+            || renderer.style().visibility() != VISIBLE)
             continue;
 
-        LayoutUnit top = renderer->borderTop() + renderer->paddingTop() + (isTableRow() ? LayoutUnit() : renderer->y());
-        LayoutUnit bottom = top + renderer->contentHeight();
-        LayoutUnit left = renderer->borderLeft() + renderer->paddingLeft() + (isTableRow() ? LayoutUnit() : renderer->x());
-        LayoutUnit right = left + renderer->contentWidth();
+        LayoutUnit top = renderer.borderTop() + renderer.paddingTop() + (is<RenderTableRow>(*this) ? LayoutUnit() : renderer.y());
+        LayoutUnit bottom = top + renderer.contentHeight();
+        LayoutUnit left = renderer.borderLeft() + renderer.paddingLeft() + (is<RenderTableRow>(*this) ? LayoutUnit() : renderer.x());
+        LayoutUnit right = left + renderer.contentWidth();
         
         if (point.x() <= right && point.x() >= left && point.y() <= top && point.y() >= bottom) {
-            if (renderer->isTableRow())
-                return renderer->positionForPoint(point + adjustedPoint - renderer->locationOffset());
-            return renderer->positionForPoint(point - renderer->locationOffset());
+            if (is<RenderTableRow>(renderer))
+                return renderer.positionForPoint(point + adjustedPoint - renderer.locationOffset(), region);
+            return renderer.positionForPoint(point - renderer.locationOffset(), region);
         }
 
         // Find the distance from (x, y) to the box.  Split the space around the box into 8 pieces
@@ -4207,13 +4499,13 @@ VisiblePosition RenderBox::positionForPoint(const LayoutPoint& point)
 
         LayoutUnit dist = difference.width() * difference.width() + difference.height() * difference.height();
         if (dist < minDist) {
-            closestRenderer = renderer;
+            closestRenderer = &renderer;
             minDist = dist;
         }
     }
     
     if (closestRenderer)
-        return closestRenderer->positionForPoint(adjustedPoint - closestRenderer->locationOffset());
+        return closestRenderer->positionForPoint(adjustedPoint - closestRenderer->locationOffset(), region);
     
     return createVisiblePosition(firstPositionInOrBeforeNode(nonPseudoElement()));
 }
@@ -4228,18 +4520,24 @@ bool RenderBox::shrinkToAvoidFloats() const
     return style().width().isAuto();
 }
 
+bool RenderBox::createsNewFormattingContext() const
+{
+    return (isInlineBlockOrInlineTable() && !isAnonymousInlineBlock()) || isFloatingOrOutOfFlowPositioned() || hasOverflowClip() || isFlexItemIncludingDeprecated()
+        || isTableCell() || isTableCaption() || isFieldset() || isWritingModeRoot() || isDocumentElementRenderer() || isRenderFlowThread() || isRenderRegion()
+        || isGridItem() || style().specifiesColumns() || style().columnSpan();
+}
+
 bool RenderBox::avoidsFloats() const
 {
-    return isReplaced() || hasOverflowClip() || isHR() || isLegend() || isWritingModeRoot() || isFlexItemIncludingDeprecated();
+    return (isReplaced() && !isAnonymousInlineBlock()) || isHR() || isLegend() || createsNewFormattingContext();
 }
 
 void RenderBox::addVisualEffectOverflow()
 {
-    if (!style().boxShadow() && !style().hasBorderImageOutsets())
+    if (!style().boxShadow() && !style().hasBorderImageOutsets() && !outlineStyleForRepaint().hasOutlineInVisualOverflow())
         return;
 
-    LayoutRect borderBox = borderBoxRect();
-    addVisualOverflow(applyVisualEffectOverflow(borderBox));
+    addVisualOverflow(applyVisualEffectOverflow(borderBoxRect()));
 
     RenderFlowThread* flowThread = flowThreadContainingBlock();
     if (flowThread)
@@ -4283,11 +4581,18 @@ LayoutRect RenderBox::applyVisualEffectOverflow(const LayoutRect& borderBox) con
         overflowMaxY = std::max(overflowMaxY, borderBox.maxY() + ((!isFlipped || !isHorizontal) ? borderOutsets.bottom() : borderOutsets.top()));
     }
 
+    if (outlineStyleForRepaint().hasOutlineInVisualOverflow()) {
+        LayoutUnit outlineSize = outlineStyleForRepaint().outlineSize();
+        overflowMinX = std::min(overflowMinX, borderBox.x() - outlineSize);
+        overflowMaxX = std::max(overflowMaxX, borderBox.maxX() + outlineSize);
+        overflowMinY = std::min(overflowMinY, borderBox.y() - outlineSize);
+        overflowMaxY = std::max(overflowMaxY, borderBox.maxY() + outlineSize);
+    }
     // Add in the final overflow with shadows and outsets combined.
     return LayoutRect(overflowMinX, overflowMinY, overflowMaxX - overflowMinX, overflowMaxY - overflowMinY);
 }
 
-void RenderBox::addOverflowFromChild(RenderBox* child, const LayoutSize& delta)
+void RenderBox::addOverflowFromChild(const RenderBox* child, const LayoutSize& delta)
 {
     // Never allow flow threads to propagate overflow up to a parent.
     if (child->isRenderFlowThread())
@@ -4316,7 +4621,7 @@ void RenderBox::addOverflowFromChild(RenderBox* child, const LayoutSize& delta)
 
 void RenderBox::addLayoutOverflow(const LayoutRect& rect)
 {
-    LayoutRect clientBox = clientBoxRect();
+    LayoutRect clientBox = flippedClientBoxRect();
     if (clientBox.contains(rect) || rect.isEmpty())
         return;
     
@@ -4357,36 +4662,69 @@ void RenderBox::addVisualOverflow(const LayoutRect& rect)
         return;
         
     if (!m_overflow)
-        m_overflow = adoptRef(new RenderOverflow(clientBoxRect(), borderBox));
+        m_overflow = adoptRef(new RenderOverflow(flippedClientBoxRect(), borderBox));
     
     m_overflow->addVisualOverflow(rect);
 }
 
 void RenderBox::clearOverflow()
 {
-    m_overflow.clear();
+    m_overflow = nullptr;
     RenderFlowThread* flowThread = flowThreadContainingBlock();
     if (flowThread)
         flowThread->clearRegionsOverflow(this);
 }
 
-inline static bool percentageLogicalHeightIsResolvable(const RenderBox* box)
+static bool logicalWidthIsResolvable(const RenderBox& renderBox)
+{
+    const RenderBox* box = &renderBox;
+    while (box && !is<RenderView>(*box) && !box->isOutOfFlowPositioned()
+        && !box->hasOverrideContainingBlockLogicalWidth()
+        && (box->style().logicalWidth().isAuto() || box->isAnonymousBlock()))
+        box = box->containingBlock();
+
+    if (box->style().logicalWidth().isFixed())
+        return true;
+    if (box->isRenderView())
+        return true;
+    // The size of the containing block of an absolutely positioned element is always definite with respect to that
+    // element (http://dev.w3.org/csswg/css-sizing-3/#definite).
+    if (box->isOutOfFlowPositioned())
+        return true;
+    if (box->hasOverrideContainingBlockLogicalWidth())
+        return static_cast<bool>(box->overrideContainingBlockContentLogicalWidth());
+    if (box->style().logicalWidth().isPercentOrCalculated())
+        return logicalWidthIsResolvable(*box->containingBlock());
+
+    return false;
+}
+
+bool RenderBox::hasDefiniteLogicalWidth() const
+{
+    return logicalWidthIsResolvable(*this);
+}
+
+inline static bool percentageLogicalHeightIsResolvable(const RenderBox& box)
 {
-    return RenderBox::percentageLogicalHeightIsResolvableFromBlock(box->containingBlock(), box->isOutOfFlowPositioned());
+    return RenderBox::percentageLogicalHeightIsResolvableFromBlock(*box.containingBlock(), box.isOutOfFlowPositioned(), box.scrollsOverflowY());
 }
 
-bool RenderBox::percentageLogicalHeightIsResolvableFromBlock(const RenderBlock* containingBlock, bool isOutOfFlowPositioned)
+bool RenderBox::percentageLogicalHeightIsResolvableFromBlock(const RenderBlock& containingBlock, bool isOutOfFlowPositioned, bool scrollsOverflowY)
 {
     // In quirks mode, blocks with auto height are skipped, and we keep looking for an enclosing
     // block that may have a specified height and then use it. In strict mode, this violates the
     // specification, which states that percentage heights just revert to auto if the containing
     // block has an auto height. We still skip anonymous containing blocks in both modes, though, and look
     // only at explicit containers.
-    const RenderBlock* cb = containingBlock;
+    const RenderBlock* cb = &containingBlock;
     bool inQuirksMode = cb->document().inQuirksMode();
-    while (!cb->isRenderView() && !cb->isBody() && !cb->isTableCell() && !cb->isOutOfFlowPositioned() && cb->style().logicalHeight().isAuto()) {
+    bool skippedAutoHeightContainingBlock = false;
+    while (cb && !is<RenderView>(*cb) && !cb->isBody() && !cb->isTableCell() && !cb->isOutOfFlowPositioned() && cb->style().logicalHeight().isAuto()) {
         if (!inQuirksMode && !cb->isAnonymousBlock())
             break;
+        if (cb->hasOverrideContainingBlockLogicalHeight())
+            return static_cast<bool>(cb->overrideContainingBlockContentLogicalHeight());
+        skippedAutoHeightContainingBlock = true;
         cb = cb->containingBlock();
     }
 
@@ -4399,18 +4737,20 @@ bool RenderBox::percentageLogicalHeightIsResolvableFromBlock(const RenderBlock*
     // Table cells violate what the CSS spec says to do with heights.  Basically we
     // don't care if the cell specified a height or not.  We just always make ourselves
     // be a percentage of the cell's current content height.
-    if (cb->isTableCell())
-        return true;
+    if (cb->isTableCell()) {
+        // Matches computePercentageLogicalHeight().
+        return skippedAutoHeightContainingBlock || cb->hasOverrideLogicalContentHeight() || tableCellShouldHaveZeroInitialSize(*cb, scrollsOverflowY);
+    }
 
     // Otherwise we only use our percentage height if our containing block had a specified
     // height.
     if (cb->style().logicalHeight().isFixed())
         return true;
-    if (cb->style().logicalHeight().isPercent() && !isOutOfFlowPositionedWithSpecifiedHeight)
-        return percentageLogicalHeightIsResolvableFromBlock(cb->containingBlock(), cb->isOutOfFlowPositioned());
+    if (cb->style().logicalHeight().isPercentOrCalculated() && !isOutOfFlowPositionedWithSpecifiedHeight)
+        return percentageLogicalHeightIsResolvableFromBlock(*cb->containingBlock(), cb->isOutOfFlowPositioned(), cb->scrollsOverflowY());
     if (cb->isRenderView() || inQuirksMode || isOutOfFlowPositionedWithSpecifiedHeight)
         return true;
-    if (cb->isRoot() && isOutOfFlowPositioned) {
+    if (cb->isDocumentElementRenderer() && isOutOfFlowPositioned) {
         // Match the positioned objects behavior, which is that positioned objects will fill their viewport
         // always.  Note we could only hit this case by recurring into computePercentageLogicalHeight on a positioned containing block.
         return true;
@@ -4419,6 +4759,23 @@ bool RenderBox::percentageLogicalHeightIsResolvableFromBlock(const RenderBlock*
     return false;
 }
 
+bool RenderBox::hasDefiniteLogicalHeight() const
+{
+    const Length& logicalHeight = style().logicalHeight();
+    if (logicalHeight.isFixed())
+        return true;
+    // The size of the containing block of an absolutely positioned element is always definite with respect to that
+    // element (http://dev.w3.org/csswg/css-sizing-3/#definite).
+    if (isOutOfFlowPositioned())
+        return true;
+    if (hasOverrideContainingBlockLogicalHeight())
+        return static_cast<bool>(overrideContainingBlockContentLogicalHeight());
+    if (logicalHeight.isIntrinsicOrAuto())
+        return false;
+
+    return percentageLogicalHeightIsResolvable(*this);
+}
+
 bool RenderBox::hasUnsplittableScrollingOverflow() const
 {
     // We will paginate as long as we don't scroll overflow in the pagination direction.
@@ -4432,16 +4789,17 @@ bool RenderBox::hasUnsplittableScrollingOverflow() const
     // conditions, but it should work out to be good enough for common cases. Paginating overflow
     // with scrollbars present is not the end of the world and is what we used to do in the old model anyway.
     return !style().logicalHeight().isIntrinsicOrAuto()
-        || (!style().logicalMaxHeight().isIntrinsicOrAuto() && !style().logicalMaxHeight().isUndefined() && (!style().logicalMaxHeight().isPercent() || percentageLogicalHeightIsResolvable(this)))
-        || (!style().logicalMinHeight().isIntrinsicOrAuto() && style().logicalMinHeight().isPositive() && (!style().logicalMinHeight().isPercent() || percentageLogicalHeightIsResolvable(this)));
+        || (!style().logicalMaxHeight().isIntrinsicOrAuto() && !style().logicalMaxHeight().isUndefined() && (!style().logicalMaxHeight().isPercentOrCalculated() || percentageLogicalHeightIsResolvable(*this)))
+        || (!style().logicalMinHeight().isIntrinsicOrAuto() && style().logicalMinHeight().isPositive() && (!style().logicalMinHeight().isPercentOrCalculated() || percentageLogicalHeightIsResolvable(*this)));
 }
 
 bool RenderBox::isUnsplittableForPagination() const
 {
-    return isReplaced() || hasUnsplittableScrollingOverflow() || (parent() && isWritingModeRoot())
-        // FIXME: Treat multi-column elements as unsplittable for now. Remove once we implement the correct
-        // fragmentation model for multicolumn.
-        || isMultiColumnBlockFlow();
+    return isReplaced()
+        || hasUnsplittableScrollingOverflow()
+        || (parent() && isWritingModeRoot())
+        || isRenderNamedFlowFragmentContainer()
+        || fixedPositionedWithNamedFlowContainingBlock();
 }
 
 LayoutUnit RenderBox::lineHeight(bool /*firstLine*/, LineDirectionMode direction, LinePositionMode /*linePositionMode*/) const
@@ -4472,7 +4830,7 @@ RenderLayer* RenderBox::enclosingFloatPaintingLayer() const
     return nullptr;
 }
 
-LayoutRect RenderBox::logicalVisualOverflowRectForPropagation(RenderStyle* parentStyle) const
+LayoutRect RenderBox::logicalVisualOverflowRectForPropagation(const RenderStyle* parentStyle) const
 {
     LayoutRect rect = visualOverflowRectForPropagation(parentStyle);
     if (!parentStyle->isHorizontalWritingMode())
@@ -4480,7 +4838,7 @@ LayoutRect RenderBox::logicalVisualOverflowRectForPropagation(RenderStyle* paren
     return rect;
 }
 
-LayoutRect RenderBox::visualOverflowRectForPropagation(RenderStyle* parentStyle) const
+LayoutRect RenderBox::visualOverflowRectForPropagation(const RenderStyle* parentStyle) const
 {
     // If the writing modes of the child and parent match, then we don't have to 
     // do anything fancy. Just return the result.
@@ -4498,7 +4856,7 @@ LayoutRect RenderBox::visualOverflowRectForPropagation(RenderStyle* parentStyle)
     return rect;
 }
 
-LayoutRect RenderBox::logicalLayoutOverflowRectForPropagation(RenderStyle* parentStyle) const
+LayoutRect RenderBox::logicalLayoutOverflowRectForPropagation(const RenderStyle* parentStyle) const
 {
     LayoutRect rect = layoutOverflowRectForPropagation(parentStyle);
     if (!parentStyle->isHorizontalWritingMode())
@@ -4506,16 +4864,16 @@ LayoutRect RenderBox::logicalLayoutOverflowRectForPropagation(RenderStyle* paren
     return rect;
 }
 
-LayoutRect RenderBox::layoutOverflowRectForPropagation(RenderStyle* parentStyle) const
+LayoutRect RenderBox::layoutOverflowRectForPropagation(const RenderStyle* parentStyle) const
 {
     // Only propagate interior layout overflow if we don't clip it.
     LayoutRect rect = borderBoxRect();
     if (!hasOverflowClip())
         rect.unite(layoutOverflowRect());
 
-    bool hasTransform = hasLayer() && layer()->transform();
+    bool hasTransform = this->hasTransform();
 #if PLATFORM(IOS)
-    if (isInFlowPositioned() || (hasTransform && document().settings()->shouldTransformsAffectOverflow())) {
+    if (isInFlowPositioned() || (hasTransform && settings().shouldTransformsAffectOverflow())) {
 #else
     if (isInFlowPositioned() || hasTransform) {
 #endif
@@ -4549,7 +4907,29 @@ LayoutRect RenderBox::layoutOverflowRectForPropagation(RenderStyle* parentStyle)
     return rect;
 }
 
-LayoutRect RenderBox::overflowRectForPaintRejection(RenderRegion* region) const
+LayoutRect RenderBox::flippedClientBoxRect() const
+{
+    // Because of the special coordinate system used for overflow rectangles (not quite logical, not
+    // quite physical), we need to flip the block progression coordinate in vertical-rl and
+    // horizontal-bt writing modes. Apart from that, this method does the same as clientBoxRect().
+
+    LayoutUnit left = borderLeft();
+    LayoutUnit top = borderTop();
+    LayoutUnit right = borderRight();
+    LayoutUnit bottom = borderBottom();
+    // Calculate physical padding box.
+    LayoutRect rect(left, top, width() - left - right, height() - top - bottom);
+    // Flip block progression axis if writing mode is vertical-rl or horizontal-bt.
+    flipForWritingMode(rect);
+    // Subtract space occupied by scrollbars. They are at their physical edge in this coordinate
+    // system, so order is important here: first flip, then subtract scrollbars.
+    if (shouldPlaceBlockDirectionScrollbarOnLeft())
+        rect.move(verticalScrollbarWidth(), 0);
+    rect.contract(verticalScrollbarWidth(), horizontalScrollbarHeight());
+    return rect;
+}
+
+LayoutRect RenderBox::overflowRectForPaintRejection(RenderNamedFlowFragment* namedFlowFragment) const
 {
     LayoutRect overflowRect = visualOverflowRect();
     
@@ -4557,22 +4937,19 @@ LayoutRect RenderBox::overflowRectForPaintRejection(RenderRegion* region) const
     // cause the paint rejection algorithm to prevent them from painting when using different width regions.
     // e.g. an absolutely positioned box with bottom:0px and right:0px would have it's frameRect.x relative
     // to the flow thread, not the last region (in which it will end up because of bottom:0px)
-    if (region) {
-        if (RenderFlowThread* flowThread = region->flowThread()) {
-            RenderRegion* startRegion = 0;
-            RenderRegion* endRegion = 0;
-            flowThread->getRegionRangeForBox(this, startRegion, endRegion);
-
-            if (startRegion && endRegion)
-                overflowRect.unite(region->visualOverflowRectForBox(this));
-        }
+    if (namedFlowFragment && namedFlowFragment->isValid()) {
+        RenderFlowThread* flowThread = namedFlowFragment->flowThread();
+        RenderRegion* startRegion = nullptr;
+        RenderRegion* endRegion = nullptr;
+        if (flowThread->getRegionRangeForBox(this, startRegion, endRegion))
+            overflowRect.unite(namedFlowFragment->visualOverflowRectForBox(*this));
     }
     
     if (!m_overflow || !usesCompositedScrolling())
         return overflowRect;
 
     overflowRect.unite(layoutOverflowRect());
-    overflowRect.move(-scrolledContentOffset());
+    overflowRect.moveBy(-scrollPosition());
     return overflowRect;
 }
 
@@ -4623,13 +5000,6 @@ LayoutPoint RenderBox::flipForWritingMode(const LayoutPoint& position) const
     return isHorizontalWritingMode() ? LayoutPoint(position.x(), height() - position.y()) : LayoutPoint(width() - position.x(), position.y());
 }
 
-LayoutPoint RenderBox::flipForWritingModeIncludingColumns(const LayoutPoint& point) const
-{
-    if (!hasColumns() || !style().isFlippedBlocksWritingMode())
-        return flipForWritingMode(point);
-    return toRenderBlock(this)->flipForWritingModeIncludingColumns(point);
-}
-
 LayoutSize RenderBox::flipForWritingMode(const LayoutSize& offset) const
 {
     if (!style().isFlippedBlocksWritingMode())
@@ -4657,6 +5027,9 @@ void RenderBox::flipForWritingMode(FloatRect& rect) const
 
 LayoutPoint RenderBox::topLeftLocation() const
 {
+    if (!view().frameView().hasFlippedBlockRenderers())
+        return location();
+    
     RenderBlock* containerBlock = containingBlock();
     if (!containerBlock || containerBlock == this)
         return location();
@@ -4665,6 +5038,9 @@ LayoutPoint RenderBox::topLeftLocation() const
 
 LayoutSize RenderBox::topLeftLocationOffset() const
 {
+    if (!view().frameView().hasFlippedBlockRenderers())
+        return locationOffset();
+
     RenderBlock* containerBlock = containingBlock();
     if (!containerBlock || containerBlock == this)
         return locationOffset();
@@ -4674,39 +5050,52 @@ LayoutSize RenderBox::topLeftLocationOffset() const
     return LayoutSize(rect.x(), rect.y());
 }
 
+void RenderBox::applyTopLeftLocationOffsetWithFlipping(LayoutPoint& point) const
+{
+    RenderBlock* containerBlock = containingBlock();
+    if (!containerBlock || containerBlock == this) {
+        point.move(m_frameRect.x(), m_frameRect.y());
+        return;
+    }
+    
+    LayoutRect rect(frameRect());
+    containerBlock->flipForWritingMode(rect); // FIXME: This is wrong if we are an absolutely positioned object  enclosed by a relative-positioned inline.
+    point.move(rect.x(), rect.y());
+}
+
 bool RenderBox::hasRelativeDimensions() const
 {
-    return style().height().isPercent() || style().width().isPercent()
-            || style().maxHeight().isPercent() || style().maxWidth().isPercent()
-            || style().minHeight().isPercent() || style().minWidth().isPercent();
+    return style().height().isPercentOrCalculated() || style().width().isPercentOrCalculated()
+        || style().maxHeight().isPercentOrCalculated() || style().maxWidth().isPercentOrCalculated()
+        || style().minHeight().isPercentOrCalculated() || style().minWidth().isPercentOrCalculated();
 }
 
 bool RenderBox::hasRelativeLogicalHeight() const
 {
-    return style().logicalHeight().isPercent()
-            || style().logicalMinHeight().isPercent()
-            || style().logicalMaxHeight().isPercent();
+    return style().logicalHeight().isPercentOrCalculated()
+        || style().logicalMinHeight().isPercentOrCalculated()
+        || style().logicalMaxHeight().isPercentOrCalculated();
 }
 
-bool RenderBox::hasViewportPercentageLogicalHeight() const
+bool RenderBox::hasRelativeLogicalWidth() const
 {
-    return style().logicalHeight().isViewportPercentage()
-        || style().logicalMinHeight().isViewportPercentage()
-        || style().logicalMaxHeight().isViewportPercentage();
+    return style().logicalWidth().isPercentOrCalculated()
+        || style().logicalMinWidth().isPercentOrCalculated()
+        || style().logicalMaxWidth().isPercentOrCalculated();
 }
 
-static void markBoxForRelayoutAfterSplit(RenderBox* box)
+static void markBoxForRelayoutAfterSplit(RenderBox& box)
 {
     // FIXME: The table code should handle that automatically. If not,
     // we should fix it and remove the table part checks.
-    if (box->isTable()) {
+    if (is<RenderTable>(box)) {
         // Because we may have added some sections with already computed column structures, we need to
         // sync the table structure with them now. This avoids crashes when adding new cells to the table.
-        toRenderTable(box)->forceSectionsRecalc();
-    } else if (box->isTableSection())
-        toRenderTableSection(box)->setNeedsCellRecalc();
+        downcast<RenderTable>(box).forceSectionsRecalc();
+    } else if (is<RenderTableSection>(box))
+        downcast<RenderTableSection>(box).setNeedsCellRecalc();
 
-    box->setNeedsLayoutAndPrefWidthsRecalc();
+    box.setNeedsLayoutAndPrefWidthsRecalc();
 }
 
 RenderObject* RenderBox::splitAnonymousBoxesAroundChild(RenderObject* beforeChild)
@@ -4714,32 +5103,32 @@ RenderObject* RenderBox::splitAnonymousBoxesAroundChild(RenderObject* beforeChil
     bool didSplitParentAnonymousBoxes = false;
 
     while (beforeChild->parent() != this) {
-        RenderBox* boxToSplit = toRenderBox(beforeChild->parent());
-        if (boxToSplit->firstChild() != beforeChild && boxToSplit->isAnonymous()) {
+        auto& boxToSplit = downcast<RenderBox>(*beforeChild->parent());
+        if (boxToSplit.firstChild() != beforeChild && boxToSplit.isAnonymous()) {
             didSplitParentAnonymousBoxes = true;
 
             // We have to split the parent box into two boxes and move children
             // from |beforeChild| to end into the new post box.
-            RenderBox* postBox = boxToSplit->createAnonymousBoxWithSameTypeAs(this);
-            postBox->setChildrenInline(boxToSplit->childrenInline());
-            RenderBox* parentBox = toRenderBox(boxToSplit->parent());
+            auto* postBox = boxToSplit.createAnonymousBoxWithSameTypeAs(*this).release();
+            postBox->setChildrenInline(boxToSplit.childrenInline());
+            RenderBox* parentBox = downcast<RenderBox>(boxToSplit.parent());
             // We need to invalidate the |parentBox| before inserting the new node
             // so that the table repainting logic knows the structure is dirty.
             // See for example RenderTableCell:clippedOverflowRectForRepaint.
-            markBoxForRelayoutAfterSplit(parentBox);
-            parentBox->insertChildInternal(postBox, boxToSplit->nextSibling(), NotifyChildren);
-            boxToSplit->moveChildrenTo(postBox, beforeChild, 0, true);
+            markBoxForRelayoutAfterSplit(*parentBox);
+            parentBox->insertChildInternal(postBox, boxToSplit.nextSibling(), NotifyChildren);
+            boxToSplit.moveChildrenTo(postBox, beforeChild, nullptr, true);
 
             markBoxForRelayoutAfterSplit(boxToSplit);
-            markBoxForRelayoutAfterSplit(postBox);
+            markBoxForRelayoutAfterSplit(*postBox);
 
             beforeChild = postBox;
         } else
-            beforeChild = boxToSplit;
+            beforeChild = &boxToSplit;
     }
 
     if (didSplitParentAnonymousBoxes)
-        markBoxForRelayoutAfterSplit(this);
+        markBoxForRelayoutAfterSplit(*this);
 
     ASSERT(beforeChild->parent() == this);
     return beforeChild;
@@ -4755,4 +5144,17 @@ LayoutUnit RenderBox::offsetFromLogicalTopOfFirstPage() const
     return containerBlock->offsetFromLogicalTopOfFirstPage() + logicalTop();
 }
 
+const RenderBox* RenderBox::findEnclosingScrollableContainer() const
+{
+    for (auto& candidate : lineageOfType<RenderBox>(*this)) {
+        if (candidate.hasOverflowClip())
+            return &candidate;
+    }
+    // If all parent elements are not overflow scrollable, check the body.
+    if (document().body() && frame().mainFrame().view() && frame().mainFrame().view()->isScrollable())
+        return document().body()->renderBox();
+    
+    return nullptr;
+}
+
 } // namespace WebCore