Blink Compositor Animation: Introduce CompositorAnimationHost correctly.

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h

Index: third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
index ea237d5316e3f3947d011ec68a8134563df0cfb8..e2bd6492b516b30a3c4ee1d4128dcbb291e88ce7 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
@@ -63,6 +63,7 @@ class HitTestResult;
 class LayoutBox;
 class LayoutScrollbarPart;
 class PaintLayer;
+class ScrollingCoordinator;
 class StickyPositionScrollingConstraints;
 class SubtreeLayoutScope;
 
@@ -291,6 +292,7 @@ class CORE_EXPORT PaintLayerScrollableArea final
   bool shouldPlaceVerticalScrollbarOnLeft() const override;
   int pageStep(ScrollbarOrientation) const override;
   ScrollBehavior scrollBehaviorStyle() const override;
+  CompositorAnimationHost* compositorAnimationHost() const override;
   CompositorAnimationTimeline* compositorAnimationTimeline() const override;
 
   void visibleSizeChanged();
@@ -519,6 +521,8 @@ class CORE_EXPORT PaintLayerScrollableArea final
 
   void updateCompositingLayersAfterScroll();
 
+  ScrollingCoordinator* getScrollingCoordinator() const;
+
   PaintLayerScrollableAreaRareData* rareData() { return m_rareData.get(); }
 
   PaintLayerScrollableAreaRareData& ensureRareData() {