Early terminate flings when scrolling impossible

public/platform/WebGestureCurveTarget.h

 /*
  * Copyright (C) 2012 Google 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 14 matching lines @@
 #ifndef WebGestureCurveTarget_h
 #define WebGestureCurveTarget_h
 
 #include "WebFloatSize.h"
 #include "WebPoint.h"
 
 namespace blink {
 
 class WebGestureCurveTarget {
 public:
-    virtual void scrollBy(const WebFloatSize& delta) = 0;
+    // TODO(jdduke): Make pure virtual when crrev.com/136173004 lands.
+    virtual bool scrollBy(const WebFloatSize& delta, const WebFloatSize& velocity) { return false; }
 
-    virtual void notifyCurrentFlingVelocity(const WebFloatSize&) { }
+    // TODO(jdduke): Remove when crrev.com/136173004 lands.
+    virtual void scrollBy(const WebFloatSize& delta) { }
+
+    // TODO(jdduke): Remove when crrev.com/136173004 lands.
+    virtual void notifyCurrentFlingVelocity(const WebFloatSize& velocity) { }
 
 protected:
     virtual ~WebGestureCurveTarget() { }
 };
 
 } // namespace blink
 
 #endif