Implement Wheel Gesture Scrolling on OSX.

content/renderer/render_widget.h

Index: content/renderer/render_widget.h
diff --git a/content/renderer/render_widget.h b/content/renderer/render_widget.h
index 59da240ad19bf70fb2419beda592e400ffda2377..0849fc12e1bc49be368cebdbcc9a3cf9fbe4ab84 100644
--- a/content/renderer/render_widget.h
+++ b/content/renderer/render_widget.h
@@ -213,6 +213,10 @@ class CONTENT_EXPORT RenderWidget
   void ObserveWheelEventAndResult(const blink::WebMouseWheelEvent& wheel_event,
                                   const gfx::Vector2dF& wheel_unused_delta,
                                   bool event_processed) override;
+  void ObserveGestureEventAndResult(const blink::WebGestureEvent& gesture_event,
+                                    const gfx::Vector2dF& unused_delta,
+                                    bool event_processed) override;
+
   void OnDidHandleKeyEvent() override;
   void OnDidOverscroll(const DidOverscrollParams& params) override;
   void OnInputEventAck(scoped_ptr<InputEventAck> input_event_ack) override;