Implement Wheel Gesture Scrolling on OSX.

ui/events/blink/input_handler_proxy.h

Index: ui/events/blink/input_handler_proxy.h
diff --git a/ui/events/blink/input_handler_proxy.h b/ui/events/blink/input_handler_proxy.h
index 32c0efc25311e463777f1c2bdc0bdcc0e21d0b4f..2da4bc9022399dbeb1356b88a5c429d6e0c59225 100644
--- a/ui/events/blink/input_handler_proxy.h
+++ b/ui/events/blink/input_handler_proxy.h
@@ -138,7 +138,12 @@ class InputHandlerProxy
       const cc::InputHandlerScrollResult& scroll_result);
 
   // Whether to use a smooth scroll animation for this event.
-  bool ShouldAnimate(const blink::WebMouseWheelEvent& event) const;
+  bool ShouldAnimate(bool has_precise_scroll_deltas) const;
+
+  // Update the elastic overscroll controller with |gesture_event|.
+  void HandleScrollElasticityOverscroll(
+      const blink::WebGestureEvent& gesture_event,
+      const cc::InputHandlerScrollResult& scroll_result);
 
   scoped_ptr<blink::WebGestureCurve> fling_curve_;
   // Parameters for the active fling animation, stored in case we need to