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diff --git a/Source/WebCore/rendering/SimpleLineLayoutCoverage.cpp b/Source/WebCore/rendering/SimpleLineLayoutCoverage.cpp
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+++ b/Source/WebCore/rendering/SimpleLineLayoutCoverage.cpp
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+/*
+ * Copyright (C) 2017 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
+ * THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+#include "SimpleLineLayoutCoverage.h"
+
+#include "Logging.h"
+#include "RenderBlockFlow.h"
+#include "RenderChildIterator.h"
+#include "RenderStyle.h"
+#include "RenderView.h"
+#include "Settings.h"
+#include "SimpleLineLayout.h"
+#include "TextStream.h"
+
+namespace WebCore {
+namespace SimpleLineLayout {
+
+#ifndef NDEBUG
+static void printReason(AvoidanceReason reason, TextStream& stream)
+{
+    switch (reason) {
+    case FlowIsInsideRegion:
+        stream << "flow is inside region";
+        break;
+    case FlowHasHorizonalWritingMode:
+        stream << "horizontal writing mode";
+        break;
+    case FlowHasOutline:
+        stream << "outline";
+        break;
+    case FlowIsRuby:
+        stream << "ruby";
+        break;
+    case FlowHasHangingPunctuation:
+        stream << "hanging punctuation";
+        break;
+    case FlowIsPaginated:
+        stream << "paginated";
+        break;
+    case FlowHasTextOverflow:
+        stream << "text-overflow";
+        break;
+    case FlowIsDepricatedFlexBox:
+        stream << "depricatedFlexBox";
+        break;
+    case FlowParentIsPlaceholderElement:
+        stream << "placeholder element";
+        break;
+    case FlowParentIsTextAreaWithWrapping:
+        stream << "wrapping textarea";
+        break;
+    case FlowHasNonSupportedChild:
+        stream << "nested renderers";
+        break;
+    case FlowHasUnsupportedFloat:
+        stream << "complicated float";
+        break;
+    case FlowHasUnsupportedUnderlineDecoration:
+        stream << "text-underline-position: under";
+        break;
+    case FlowHasJustifiedNonLatinText:
+        stream << "text-align: justify with non-latin text";
+        break;
+    case FlowHasOverflowNotVisible:
+        stream << "overflow: hidden | scroll | auto";
+        break;
+    case FlowHasWebKitNBSPMode:
+        stream << "-webkit-nbsp-mode: space";
+        break;
+    case FlowIsNotLTR:
+        stream << "dir is not LTR";
+        break;
+    case FlowHasLineBoxContainProperty:
+        stream << "line-box-contain value indicates variable line height";
+        break;
+    case FlowIsNotTopToBottom:
+        stream << "non top-to-bottom flow";
+        break;
+    case FlowHasLineBreak:
+        stream << "line-break property";
+        break;
+    case FlowHasNonNormalUnicodeBiDi:
+        stream << "non-normal Unicode bidi";
+        break;
+    case FlowHasRTLOrdering:
+        stream << "-webkit-rtl-ordering";
+        break;
+    case FlowHasLineAlignEdges:
+        stream << "-webkit-line-align edges";
+        break;
+    case FlowHasLineSnap:
+        stream << "-webkit-line-snap property";
+        break;
+    case FlowHasTextEmphasisFillOrMark:
+        stream << "text-emphasis (fill/mark)";
+        break;
+    case FlowHasPseudoFirstLine:
+        stream << "first-line";
+        break;
+    case FlowHasPseudoFirstLetter:
+        stream << "first-letter";
+        break;
+    case FlowHasTextCombine:
+        stream << "text combine";
+        break;
+    case FlowHasTextFillBox:
+        stream << "background-color (text-fill)";
+        break;
+    case FlowHasBorderFitLines:
+        stream << "-webkit-border-fit";
+        break;
+    case FlowHasNonAutoLineBreak:
+        stream << "line-break is not auto";
+        break;
+    case FlowHasNonAutoTrailingWord:
+        stream << "-apple-trailing-word is not auto";
+        break;
+    case FlowHasSVGFont:
+        stream << "SVG font";
+        break;
+    case FlowTextHasSoftHyphen:
+        stream << "soft hyphen character";
+        break;
+    case FlowTextHasDirectionCharacter:
+        stream << "direction character";
+        break;
+    case FlowIsMissingPrimaryFont:
+        stream << "missing primary font";
+        break;
+    case FlowPrimaryFontIsInsufficient:
+        stream << "missing glyph or glyph needs another font";
+        break;
+    case FlowTextIsCombineText:
+        stream << "text is combine";
+        break;
+    case FlowTextIsRenderCounter:
+        stream << "unsupported RenderCounter";
+        break;
+    case FlowTextIsRenderQuote:
+        stream << "unsupported RenderQuote";
+        break;
+    case FlowTextIsTextFragment:
+        stream << "unsupported TextFragment";
+        break;
+    case FlowTextIsSVGInlineText:
+        stream << "unsupported SVGInlineText";
+        break;
+    case FlowHasComplexFontCodePath:
+        stream << "text with complex font codepath";
+        break;
+    case FlowHasTextShadow:
+        stream << "text-shadow";
+        break;
+    case FlowChildIsSelected:
+        stream << "selected content";
+        break;
+    case FlowFontHasOverflowGlyph:
+        stream << "-webkit-line-box-contain: glyphs with overflowing text.";
+        break;
+    case FlowTextHasSurrogatePair:
+        stream << "surrogate pair";
+        break;
+    case FlowTextIsEmpty:
+    case FlowHasNoChild:
+    case FlowHasNoParent:
+    case FeatureIsDisabled:
+    default:
+        break;
+    }
+}
+
+static void printReasons(AvoidanceReasonFlags reasons, TextStream& stream)
+{
+    bool first = true;
+    for (auto reasonItem = EndOfReasons >> 1; reasonItem != NoReason; reasonItem >>= 1) {
+        if (!(reasons & reasonItem))
+            continue;
+        stream << (first ? " " : ", ");
+        first = false;
+        printReason(reasonItem, stream);
+    }
+}
+
+static void printTextForSubtree(const RenderObject& renderer, unsigned& charactersLeft, TextStream& stream)
+{
+    if (!charactersLeft)
+        return;
+    if (is<RenderText>(renderer)) {
+        String text = downcast<RenderText>(renderer).text();
+        text = text.stripWhiteSpace();
+        unsigned len = std::min(charactersLeft, text.length());
+        stream << text.left(len);
+        charactersLeft -= len;
+        return;
+    }
+    if (!is<RenderElement>(renderer))
+        return;
+    for (const auto* child = downcast<RenderElement>(renderer).firstChild(); child; child = child->nextSibling())
+        printTextForSubtree(*child, charactersLeft, stream);
+}
+
+static unsigned textLengthForSubtree(const RenderObject& renderer)
+{
+    if (is<RenderText>(renderer))
+        return downcast<RenderText>(renderer).textLength();
+    if (!is<RenderElement>(renderer))
+        return 0;
+    unsigned textLength = 0;
+    for (const auto* child = downcast<RenderElement>(renderer).firstChild(); child; child = child->nextSibling())
+        textLength += textLengthForSubtree(*child);
+    return textLength;
+}
+
+static void collectNonEmptyLeafRenderBlockFlows(const RenderObject& renderer, HashSet<const RenderBlockFlow*>& leafRenderers)
+{
+    if (is<RenderText>(renderer)) {
+        if (!downcast<RenderText>(renderer).textLength())
+            return;
+        // Find RenderBlockFlow ancestor.
+        for (const auto* current = renderer.parent(); current; current = current->parent()) {
+            if (!is<RenderBlockFlow>(current))
+                continue;
+            leafRenderers.add(downcast<RenderBlockFlow>(current));
+            break;
+        }
+        return;
+    }
+    if (!is<RenderElement>(renderer))
+        return;
+    for (const auto* child = downcast<RenderElement>(renderer).firstChild(); child; child = child->nextSibling())
+        collectNonEmptyLeafRenderBlockFlows(*child, leafRenderers);
+}
+
+static void collectNonEmptyLeafRenderBlockFlowsForCurrentPage(HashSet<const RenderBlockFlow*>& leafRenderers)
+{
+    for (const auto* document : Document::allDocuments()) {
+        if (!document->renderView() || document->pageCacheState() != Document::NotInPageCache)
+            continue;
+        if (!document->isHTMLDocument() && !document->isXHTMLDocument())
+            continue;
+        collectNonEmptyLeafRenderBlockFlows(*document->renderView(), leafRenderers);
+    }
+}
+
+void toggleSimpleLineLayout()
+{
+    for (auto* document : Document::allDocuments()) {
+        auto& settings = document->mutableSettings();
+        settings.setSimpleLineLayoutEnabled(!settings.simpleLineLayoutEnabled());
+    }
+}
+
+void printSimpleLineLayoutBlockList()
+{
+    HashSet<const RenderBlockFlow*> leafRenderers;
+    collectNonEmptyLeafRenderBlockFlowsForCurrentPage(leafRenderers);
+    if (!leafRenderers.size()) {
+        WTFLogAlways("No text found in this document\n");
+        return;
+    }
+    TextStream stream;
+    stream << "---------------------------------------------------\n";
+    for (const auto* flow : leafRenderers) {
+        auto reason = canUseForWithReason(*flow, IncludeReasons::All);
+        if (reason == NoReason)
+            continue;
+        unsigned printedLength = 30;
+        stream << "\"";
+        printTextForSubtree(*flow, printedLength, stream);
+        for (;printedLength > 0; --printedLength)
+            stream << " ";
+        stream << "\"(" << textLengthForSubtree(*flow) << "):";
+        printReasons(reason, stream);
+        stream << "\n";
+    }
+    stream << "---------------------------------------------------\n";
+    WTFLogAlways("%s", stream.release().utf8().data());
+}
+
+void printSimpleLineLayoutCoverage()
+{
+    HashSet<const RenderBlockFlow*> leafRenderers;
+    collectNonEmptyLeafRenderBlockFlowsForCurrentPage(leafRenderers);
+    if (!leafRenderers.size()) {
+        WTFLogAlways("No text found in this document\n");
+        return;
+    }
+    TextStream stream;
+    HashMap<AvoidanceReason, unsigned> flowStatistics;
+    unsigned textLength = 0;
+    unsigned unsupportedTextLength = 0;
+    unsigned numberOfUnsupportedLeafBlocks = 0;
+    unsigned supportedButForcedToLineLayoutTextLength = 0;
+    unsigned numberOfSupportedButForcedToLineLayoutLeafBlocks = 0;
+    for (const auto* flow : leafRenderers) {
+        auto flowLength = textLengthForSubtree(*flow);
+        textLength += flowLength;
+        auto reasons = canUseForWithReason(*flow, IncludeReasons::All);
+        if (reasons == NoReason) {
+            if (flow->lineLayoutPath() == RenderBlockFlow::ForceLineBoxesPath) {
+                supportedButForcedToLineLayoutTextLength += flowLength;
+                ++numberOfSupportedButForcedToLineLayoutLeafBlocks;
+            }
+            continue;
+        }
+        ++numberOfUnsupportedLeafBlocks;
+        unsupportedTextLength += flowLength;
+        for (auto reasonItem = EndOfReasons >> 1; reasonItem != NoReason; reasonItem >>= 1) {
+            if (!(reasons & reasonItem))
+                continue;
+            auto result = flowStatistics.add(reasonItem, flowLength);
+            if (!result.isNewEntry)
+                result.iterator->value += flowLength;
+        }
+    }
+    stream << "---------------------------------------------------\n";
+    stream << "Number of blocks: total(" <<  leafRenderers.size() << ") non-simple(" << numberOfUnsupportedLeafBlocks << ")\nContent length: total(" <<
+        textLength << ") non-simple(" << unsupportedTextLength << ")\n";
+    for (const auto reasonEntry : flowStatistics) {
+        printReason(reasonEntry.key, stream);
+        stream << ": " << (float)reasonEntry.value / (float)textLength * 100 << "%\n";
+    }
+    if (supportedButForcedToLineLayoutTextLength) {
+        stream << "Simple line layout potential coverage: " << (float)(textLength - unsupportedTextLength) / (float)textLength * 100 << "%\n\n";
+        stream << "Simple line layout actual coverage: " << (float)(textLength - unsupportedTextLength - supportedButForcedToLineLayoutTextLength) / (float)textLength * 100 << "%\nForced line layout blocks: " << numberOfSupportedButForcedToLineLayoutLeafBlocks << " content length: " << supportedButForcedToLineLayoutTextLength << "(" << (float)supportedButForcedToLineLayoutTextLength / (float)textLength * 100 << "%)";
+    } else
+        stream << "Simple line layout coverage: " << (float)(textLength - unsupportedTextLength) / (float)textLength * 100 << "%";
+    stream << "\n---------------------------------------------------\n";
+    WTFLogAlways("%s", stream.release().utf8().data());
+}
+#endif
+
+}
+}