Early terminate flings when scrolling impossible

content/renderer/input/input_handler_proxy.h

 // Copyright 2013 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 CONTENT_RENDERER_INPUT_INPUT_HANDLER_PROXY_H_
 #define CONTENT_RENDERER_INPUT_INPUT_HANDLER_PROXY_H_
 
 #include "base/basictypes.h"
 #include "base/containers/hash_tables.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 28 matching lines @@
   };
   EventDisposition HandleInputEventWithLatencyInfo(
       const blink::WebInputEvent& event,
       ui::LatencyInfo* latency_info);
   EventDisposition HandleInputEvent(const blink::WebInputEvent& event);
 
   // cc::InputHandlerClient implementation.
   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_;
   }
 
  private:
   EventDisposition HandleGestureFling(const blink::WebGestureEvent& event);
 
   // Returns true if we scrolled by the increment.
   bool TouchpadFlingScroll(const blink::WebFloatSize& increment);
@@ skipping 17 matching lines @@
   // This is always false when there are no flings on the main thread, but
   // conservative in the sense that we might not be actually flinging when it is
   // true.
   bool fling_may_be_active_on_main_thread_;
   // The axes on which the current fling is allowed to scroll.  If a given fling
   // has overscrolled on a particular axis, further fling scrolls on that axis
   // will be disabled.
   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);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_INPUT_INPUT_HANDLER_PROXY_H_