[RootLayerScrolls] Fix frame scrolling layer in ScrollingCoordinator

third_party/WebKit/Source/platform/scroll/ScrollableArea.h

 /*
  * Copyright (C) 2008, 2011 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
@@ skipping 301 matching lines @@
   // corner is setNeedsPaintInvalidation.
   virtual void scrollControlWasSetNeedsPaintInvalidation() = 0;
 
   // Returns the default scroll style this area should scroll with when not
   // explicitly specified. E.g. The scrolling behavior of an element can be
   // specified in CSS.
   virtual ScrollBehavior scrollBehaviorStyle() const {
     return ScrollBehaviorInstant;
   }
 
+  virtual bool isScrollable() const { return true; }
+
   // TODO(bokan): FrameView::setScrollOffset uses updateScrollbars to scroll
   // which bails out early if its already in updateScrollbars, the effect being
   // that programmatic scrolls (i.e. setScrollOffset) are disabled when in
   // updateScrollbars. Expose this here to allow RootFrameViewport to match the
   // semantics for now but it should be cleaned up at the source.
   virtual bool isProgrammaticallyScrollable() { return true; }
 
   // Subtracts space occupied by this ScrollableArea's scrollbars.
   // Does nothing if overlay scrollbars are enabled.
   IntSize excludeScrollbars(const IntSize&) const;
@@ skipping 114 matching lines @@
   // vertical-lr / ltr            NO                      NO
   // vertical-lr / rtl            NO                      YES
   // vertical-rl / ltr            YES                     NO
   // vertical-rl / rtl            YES                     YES
   IntPoint m_scrollOrigin;
 };
 
 }  // namespace blink
 
 #endif  // ScrollableArea_h