Don't include scroll offset in offsetFromLayoutObject for scrolling contents layers.

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h

Index: third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h
index 7a9e6e537ae852acc77d46b34645018d4045ab4e..3cb13a2426113fc0cbabb786f862990589e0655c 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h
@@ -128,6 +128,8 @@ public:
     void setContentsNeedDisplay();
     // LayoutRect is in the coordinate space of the layer's layout object.
     void setContentsNeedDisplayInRect(const LayoutRect&, PaintInvalidationReason, const DisplayItemClient&);
+    // Invalidates just scrolling content layers.
+    void setScrollingContentsNeedDisplayInRect(const LayoutRect&, PaintInvalidationReason, const DisplayItemClient&);
 
     // This is called only if we are tracking paint invalidation for testing, or ENABLE(ASSERT)
     // for error checking and debugging.
@@ -216,6 +218,8 @@ public:
 
     void updateScrollingBlockSelection();
 
+    void adjustForCompositedScrolling(const GraphicsLayer*, IntSize& offset) const;
+
 private:
     IntRect recomputeInterestRect(const GraphicsLayer*) const;
     static bool interestRectChangedEnoughToRepaint(const IntRect& previousInterestRect, const IntRect& newInterestRect, const IntSize& layerSize);
@@ -440,6 +444,11 @@ private:
     LayoutRect m_compositedBounds;
 
     LayoutSize m_contentOffsetInCompositingLayer;
+
+    // We keep track of the scrolling contents offset, so that when it changes we can notify the ScrollingCoordinator, which
+    // passes on main-thread scrolling updates to the compositor.
+    DoubleSize m_scrollingContentsOffset;
+
     unsigned m_contentOffsetInCompositingLayerDirty : 1;
 
     unsigned m_pendingUpdateScope : 2;