Coalesce async touch move events until the ack back from render

content/browser/renderer_host/input/input_router_impl.h

Index: content/browser/renderer_host/input/input_router_impl.h
diff --git a/content/browser/renderer_host/input/input_router_impl.h b/content/browser/renderer_host/input/input_router_impl.h
index 1abe33b6ad728fda3601ee28722f87e1874aa247..335e96c8a2a6f30ebfa86b3aa5956445891e48f4 100644
--- a/content/browser/renderer_host/input/input_router_impl.h
+++ b/content/browser/renderer_host/input/input_router_impl.h
@@ -145,6 +145,7 @@ private:
   void ProcessInputEventAck(blink::WebInputEvent::Type event_type,

[jdduke (slow), 2015/05/01 19:11:09]

What if we add a

struct InputEventAck {
  type, state, latency, overscroll, unique_touch;
};

with a few helper constructors? We could put that in content/common/input.
Thoughts? That would simplify a number of these functions, and eventually will
let us generalize the ack quite simply.

                             InputEventAckState ack_result,
                             const ui::LatencyInfo& latency_info,
+                            const uint32 unique_touch_event_id,
                             AckSource ack_source);
 
   // Dispatches the ack'ed event to |ack_handler_|.
@@ -169,7 +170,8 @@ private:
   // Forwards the event ack to |touch_event_queue_|, potentially triggering
   // dispatch of queued touch events, or the creation of gesture events.
   void ProcessTouchAck(InputEventAckState ack_result,
-                       const ui::LatencyInfo& latency);
+                       const ui::LatencyInfo& latency,
+                       const uint32 unique_touch_event_id);
 
   // Called when a touch timeout-affecting bit has changed, in turn toggling the
   // touch ack timeout feature of the |touch_event_queue_| as appropriate. Input