Implement overlay scrollbar fade out for non-composited scrollers.

third_party/WebKit/Source/core/frame/RootFrameViewport.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef RootFrameViewport_h
 #define RootFrameViewport_h
 
 #include "core/CoreExport.h"
 #include "platform/scroll/ScrollableArea.h"
 
@@ skipping 83 matching lines @@
   int verticalScrollbarWidth(
       OverlayScrollbarClipBehavior = IgnoreOverlayScrollbarSize) const override;
   ScrollResult userScroll(ScrollGranularity, const FloatSize&) override;
   bool scrollAnimatorEnabled() const override;
   HostWindow* getHostWindow() const override;
   void serviceScrollAnimations(double) override;
   void updateCompositorScrollAnimations() override;
   void cancelProgrammaticScrollAnimation() override;
   ScrollBehavior scrollBehaviorStyle() const override;
   Widget* getWidget() override;
-  void clearScrollAnimators() override;
+  void clearScrollableArea() override;
   LayoutBox* layoutBox() const override;
   FloatQuad localToVisibleContentQuad(const FloatQuad&,
                                       const LayoutObject*,
                                       unsigned = 0) const final;
 
  private:
   RootFrameViewport(ScrollableArea& visualViewport,
                     ScrollableArea& layoutViewport);
 
   enum ViewportToScrollFirst { VisualViewport, LayoutViewport };
@@ skipping 21 matching lines @@
 
 DEFINE_TYPE_CASTS(RootFrameViewport,
                   ScrollableArea,
                   scrollableArea,
                   scrollableArea->isRootFrameViewport(),
                   scrollableArea.isRootFrameViewport());
 
 }  // namespace blink
 
 #endif  // RootFrameViewport_h