FrameView now notifies ScrollCoorinator of changes in its scrollable area set

Source/core/frame/FrameView.h

Index: Source/core/frame/FrameView.h
diff --git a/Source/core/frame/FrameView.h b/Source/core/frame/FrameView.h
index fbda1aa028e1f244e0e6847a8c9342750d23fbaf..e80eb7b6322d5aeb06790b8a16e790c8ea7a6ac0 100644
--- a/Source/core/frame/FrameView.h
+++ b/Source/core/frame/FrameView.h
@@ -59,6 +59,7 @@ class RenderObject;
 class RenderPart;
 class RenderScrollbarPart;
 class RenderView;
+class ScrollingCoordinator;
 struct CompositedSelectionBound;
 
 typedef unsigned long long DOMTimeStamp;
@@ -685,6 +686,8 @@ private:
 
     bool isFrameViewScrollbar(const Widget* child) const { return horizontalScrollbar() == child || verticalScrollbar() == child; }
 
+    ScrollingCoordinator* scrollingCoordinator();
+
     static double s_currentFrameTimeStamp; // used for detecting decoded resource thrash in the cache
 
     LayoutSize m_size;