Implement Wheel Gesture Scrolling on OSX.

content/browser/renderer_host/input/mouse_wheel_event_queue.h

Index: content/browser/renderer_host/input/mouse_wheel_event_queue.h
diff --git a/content/browser/renderer_host/input/mouse_wheel_event_queue.h b/content/browser/renderer_host/input/mouse_wheel_event_queue.h
index b5ad7f2dcb3829af51e750325f346c33dea0575c..a224b9e2a79a446d99a711b227520ffe4092a352 100644
--- a/content/browser/renderer_host/input/mouse_wheel_event_queue.h
+++ b/content/browser/renderer_host/input/mouse_wheel_event_queue.h
@@ -17,7 +17,9 @@ namespace content {
 
 // The duration in which a ScrollEnd will be sent after the last
 // ScrollUpdate was sent for wheel based gesture scrolls.
-const int64_t kDefaultWheelScrollTransactionMs = 100;
+// Set the default wheel transaction to 0ms until
+// crbug.com/526463 is fully implemented.
+const int64_t kDefaultWheelScrollTransactionMs = 0;  // 100;
 
 class QueuedWebMouseWheelEvent;
 
@@ -76,16 +78,24 @@ class CONTENT_EXPORT MouseWheelEventQueue {
 
  private:
   void TryForwardNextEventToRenderer();
-  void SendScrollEnd(blink::WebGestureEvent update_event);
-  void SendGesture(const GestureEventWithLatencyInfo& gesture);
+  void SendScrollEnd(blink::WebGestureEvent update_event, bool synthetic);
+  void SendScrollBegin(const GestureEventWithLatencyInfo& gesture_update,
+                       bool synthetic);
 
   MouseWheelEventQueueClient* client_;
-  bool needs_scroll_begin_;
   base::OneShotTimer scroll_end_timer_;
 
   typedef std::deque<QueuedWebMouseWheelEvent*> WheelEventQueue;
   WheelEventQueue wheel_queue_;
   scoped_ptr<QueuedWebMouseWheelEvent> event_sent_for_gesture_ack_;
+
+  // True if a non-synthetic GSB needs to be sent before a GSU is sent.
+  bool needs_scroll_begin_;
+
+  // True if a non-synthetic GSE needs to be sent because a non-synthetic
+  // GSB has been sent in the past.
+  bool needs_scroll_end_;
+
   bool send_gestures_;
   int64_t scroll_transaction_ms_;
   blink::WebGestureDevice scrolling_device_;