Make tapDown async.

content/browser/renderer_host/input/immediate_input_router.cc

Index: content/browser/renderer_host/input/immediate_input_router.cc
diff --git a/content/browser/renderer_host/input/immediate_input_router.cc b/content/browser/renderer_host/input/immediate_input_router.cc
index a4c69054fd16cb8838053438b95b287a81ae904c..6ea8bdf02f172b0641a8a83be8e51c7a7bd96663 100644
--- a/content/browser/renderer_host/input/immediate_input_router.cc
+++ b/content/browser/renderer_host/input/immediate_input_router.cc
@@ -485,7 +485,7 @@ void ImmediateInputRouter::ProcessInputEventAck(
   } else if (WebInputEvent::isTouchEventType(type)) {
     ProcessTouchAck(ack_result, latency_info);
   } else if (WebInputEvent::isGestureEventType(type)) {
-    ProcessGestureAck(type, ack_result);
+    ProcessGestureAck(event_type, ack_result);
   }
 
   // WARNING: |this| may be deleted at this point.
@@ -541,8 +541,10 @@ void ImmediateInputRouter::ProcessWheelAck(InputEventAckState ack_result) {
   }
 }
 
-void ImmediateInputRouter::ProcessGestureAck(int type,
+void ImmediateInputRouter::ProcessGestureAck(WebInputEvent::Type type,
                                              InputEventAckState ack_result) {
+  if (GestureEventFilter::IsGestureEventTypeAsync(type))
+    return;

[jdduke (slow), 2013/10/01 17:16:15]

As we discussed, please add a comment here indicating the importance of order
for ack dispatch to |ack_handler_| and |gesture_event_filter_|, so somebody
doesn't fiddle with this condition.

[tdresser, 2013/10/01 17:54:36]

Done.

   const bool processed = (INPUT_EVENT_ACK_STATE_CONSUMED == ack_result);
   ack_handler_->OnGestureEventAck(
       gesture_event_filter_->GetGestureEventAwaitingAck(), ack_result);