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diff --git a/Source/WebCore/page/scrolling/ThreadedScrollingTree.cpp b/Source/WebCore/page/scrolling/ThreadedScrollingTree.cpp
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+++ b/Source/WebCore/page/scrolling/ThreadedScrollingTree.cpp
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+/*
+ * Copyright (C) 2014-2015 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 "ThreadedScrollingTree.h"
+
+#if ENABLE(ASYNC_SCROLLING)
+
+#include "AsyncScrollingCoordinator.h"
+#include "PlatformWheelEvent.h"
+#include "ScrollingThread.h"
+#include "ScrollingTreeFixedNode.h"
+#include "ScrollingTreeNode.h"
+#include "ScrollingTreeScrollingNode.h"
+#include "ScrollingTreeStickyNode.h"
+#include <wtf/RunLoop.h>
+
+namespace WebCore {
+
+ThreadedScrollingTree::ThreadedScrollingTree(AsyncScrollingCoordinator& scrollingCoordinator)
+    : m_scrollingCoordinator(&scrollingCoordinator)
+{
+}
+
+ThreadedScrollingTree::~ThreadedScrollingTree()
+{
+    // invalidate() should have cleared m_scrollingCoordinator.
+    ASSERT(!m_scrollingCoordinator);
+}
+
+ScrollingTree::EventResult ThreadedScrollingTree::tryToHandleWheelEvent(const PlatformWheelEvent& wheelEvent)
+{
+    if (shouldHandleWheelEventSynchronously(wheelEvent))
+        return SendToMainThread;
+
+    if (willWheelEventStartSwipeGesture(wheelEvent))
+        return DidNotHandleEvent;
+
+    RefPtr<ThreadedScrollingTree> protectedThis(this);
+    ScrollingThread::dispatch([protectedThis, wheelEvent] {
+        protectedThis->handleWheelEvent(wheelEvent);
+    });
+    
+    return DidHandleEvent;
+}
+
+void ThreadedScrollingTree::handleWheelEvent(const PlatformWheelEvent& wheelEvent)
+{
+    ASSERT(ScrollingThread::isCurrentThread());
+    ScrollingTree::handleWheelEvent(wheelEvent);
+}
+
+void ThreadedScrollingTree::invalidate()
+{
+    // Invalidate is dispatched by the ScrollingCoordinator class on the ScrollingThread
+    // to break the reference cycle between ScrollingTree and ScrollingCoordinator when the
+    // ScrollingCoordinator's page is destroyed.
+    ASSERT(ScrollingThread::isCurrentThread());
+
+    // Since this can potentially be the last reference to the scrolling coordinator,
+    // we need to release it on the main thread since it has member variables (such as timers)
+    // that expect to be destroyed from the main thread.
+    RunLoop::main().dispatch([scrollingCoordinator = WTFMove(m_scrollingCoordinator)] {
+    });
+}
+
+void ThreadedScrollingTree::commitTreeState(std::unique_ptr<ScrollingStateTree> scrollingStateTree)
+{
+    ASSERT(ScrollingThread::isCurrentThread());
+    ScrollingTree::commitTreeState(WTFMove(scrollingStateTree));
+}
+
+void ThreadedScrollingTree::scrollingTreeNodeDidScroll(ScrollingNodeID nodeID, const FloatPoint& scrollPosition, const std::optional<FloatPoint>& layoutViewportOrigin, ScrollingLayerPositionAction scrollingLayerPositionAction)
+{
+    if (!m_scrollingCoordinator)
+        return;
+
+    if (nodeID == rootNode()->scrollingNodeID())
+        setMainFrameScrollPosition(scrollPosition);
+
+    RunLoop::main().dispatch([scrollingCoordinator = m_scrollingCoordinator, nodeID, scrollPosition, layoutViewportOrigin, localIsHandlingProgrammaticScroll = isHandlingProgrammaticScroll(), scrollingLayerPositionAction] {
+        scrollingCoordinator->scheduleUpdateScrollPositionAfterAsyncScroll(nodeID, scrollPosition, layoutViewportOrigin, localIsHandlingProgrammaticScroll, scrollingLayerPositionAction);
+    });
+}
+
+void ThreadedScrollingTree::currentSnapPointIndicesDidChange(ScrollingNodeID nodeID, unsigned horizontal, unsigned vertical)
+{
+    if (!m_scrollingCoordinator)
+        return;
+
+    RunLoop::main().dispatch([scrollingCoordinator = m_scrollingCoordinator, nodeID, horizontal, vertical] {
+        scrollingCoordinator->setActiveScrollSnapIndices(nodeID, horizontal, vertical);
+    });
+}
+
+#if PLATFORM(MAC)
+void ThreadedScrollingTree::handleWheelEventPhase(PlatformWheelEventPhase phase)
+{
+    if (!m_scrollingCoordinator)
+        return;
+
+    RunLoop::main().dispatch([scrollingCoordinator = m_scrollingCoordinator, phase] {
+        scrollingCoordinator->handleWheelEventPhase(phase);
+    });
+}
+
+void ThreadedScrollingTree::setActiveScrollSnapIndices(ScrollingNodeID nodeID, unsigned horizontalIndex, unsigned verticalIndex)
+{
+    if (!m_scrollingCoordinator)
+        return;
+    
+    RunLoop::main().dispatch([scrollingCoordinator = m_scrollingCoordinator, nodeID, horizontalIndex, verticalIndex] {
+        scrollingCoordinator->setActiveScrollSnapIndices(nodeID, horizontalIndex, verticalIndex);
+    });
+}
+
+void ThreadedScrollingTree::deferTestsForReason(WheelEventTestTrigger::ScrollableAreaIdentifier identifier, WheelEventTestTrigger::DeferTestTriggerReason reason)
+{
+    if (!m_scrollingCoordinator)
+        return;
+
+    RunLoop::main().dispatch([scrollingCoordinator = m_scrollingCoordinator, identifier, reason] {
+        scrollingCoordinator->deferTestsForReason(identifier, reason);
+    });
+}
+
+void ThreadedScrollingTree::removeTestDeferralForReason(WheelEventTestTrigger::ScrollableAreaIdentifier identifier, WheelEventTestTrigger::DeferTestTriggerReason reason)
+{
+    if (!m_scrollingCoordinator)
+        return;
+    
+    RunLoop::main().dispatch([scrollingCoordinator = m_scrollingCoordinator, identifier, reason] {
+        scrollingCoordinator->removeTestDeferralForReason(identifier, reason);
+    });
+}
+
+#endif
+
+} // namespace WebCore
+
+#endif // ENABLE(ASYNC_SCROLLING)