Revert of Revert of Early terminate flings when scrolling impossible

content/renderer/input/input_handler_proxy.h

Index: content/renderer/input/input_handler_proxy.h
diff --git a/content/renderer/input/input_handler_proxy.h b/content/renderer/input/input_handler_proxy.h
index 0a0b2466bcacb049afb58039752dd40cacafd238..b480d45e8fb3b443f93718b7525ba1b88654293d 100644
--- a/content/renderer/input/input_handler_proxy.h
+++ b/content/renderer/input/input_handler_proxy.h
@@ -46,11 +46,13 @@
   virtual void WillShutdown() OVERRIDE;
   virtual void Animate(base::TimeTicks time) OVERRIDE;
   virtual void MainThreadHasStoppedFlinging() OVERRIDE;
-  virtual void DidOverscroll(const cc::DidOverscrollParams& params) OVERRIDE;
+  virtual void DidOverscroll(const gfx::Vector2dF& accumulated_overscroll,
+                             const gfx::Vector2dF& latest_overscroll_delta)
+      OVERRIDE;
 
   // blink::WebGestureCurveTarget implementation.
-  virtual void scrollBy(const blink::WebFloatSize& offset);
-  virtual void notifyCurrentFlingVelocity(const blink::WebFloatSize& velocity);
+  virtual bool scrollBy(const blink::WebFloatSize& offset,
+                        const blink::WebFloatSize& velocity);
 
   bool gesture_scroll_on_impl_thread_for_testing() const {
     return gesture_scroll_on_impl_thread_;
@@ -88,6 +90,9 @@
   bool disallow_horizontal_fling_scroll_;
   bool disallow_vertical_fling_scroll_;
 
+  // Non-zero only within the scope of |scrollBy|.
+  gfx::Vector2dF current_fling_velocity_;
+
   DISALLOW_COPY_AND_ASSIGN(InputHandlerProxy);
 };