Don't throttle touch events on resent GestureScrollUpdates.

content/browser/renderer_host/input/touch_event_queue.cc

Index: content/browser/renderer_host/input/touch_event_queue.cc
diff --git a/content/browser/renderer_host/input/touch_event_queue.cc b/content/browser/renderer_host/input/touch_event_queue.cc
index 35b1657048ba5635cf1ffbba8c353f8687b94359..2acae93c2cefbb03adf02c25cc3862d7b937fe57 100644
--- a/content/browser/renderer_host/input/touch_event_queue.cc
+++ b/content/browser/renderer_host/input/touch_event_queue.cc
@@ -637,7 +637,7 @@ void TouchEventQueue::OnGestureScrollEvent(
   }
 
   if (gesture_event.event.type == blink::WebInputEvent::GestureScrollUpdate)
-    send_touch_events_async_ = true;
+    send_touch_events_async_ = (gesture_event.event.resendingPluginId == -1);

[jdduke (slow), 2015/09/30 20:26:46]

Can't the resending and non-resending events be interleaved? So then shouldn't
we just ignore GSU's that have an invalid resendingPluginId (rather than turning
the asyns sending on/off)?

 }
 
 void TouchEventQueue::OnGestureEventAck(
@@ -650,7 +650,8 @@ void TouchEventQueue::OnGestureEventAck(
   // A valid |pending_async_touchmove_| will be flushed when the next event is
   // forwarded.
   if (event.event.type == blink::WebInputEvent::GestureScrollUpdate)
-    send_touch_events_async_ = (ack_result == INPUT_EVENT_ACK_STATE_CONSUMED);
+    send_touch_events_async_ = (ack_result == INPUT_EVENT_ACK_STATE_CONSUMED) &&
+                               (event.event.resendingPluginId == -1);
 }
 
 void TouchEventQueue::OnHasTouchEventHandlers(bool has_handlers) {