Don't throttle touch events on resent GestureScrollUpdates.

content/browser/renderer_host/input/touch_event_queue.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/renderer_host/input/touch_event_queue.h"
 
 #include "base/auto_reset.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/stl_util.h"
 #include "base/trace_event/trace_event.h"
@@ skipping 619 matching lines @@
       DCHECK(!touchmove_slop_suppressor_->suppressing_touchmoves())
           <<  "A touch handler should be offered a touchmove before scrolling.";
     }
 
     pending_async_touchmove_.reset();
 
     return;
   }
 
   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(
     const GestureEventWithLatencyInfo& event,
     InputEventAckState ack_result) {
   // Throttle sending touchmove events as long as the scroll events are handled.
   // Note that there's no guarantee that this ACK is for the most recent
   // gesture event (or even part of the current sequence).  Worst case, the
   // delay in updating the absorption state will result in minor UI glitches.
   // 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) {
   DCHECK(!dispatching_touch_ack_);
   DCHECK(!dispatching_touch_);
   has_handlers_ = has_handlers;
 }
 
 bool TouchEventQueue::IsPendingAckTouchStart() const {
   DCHECK(!dispatching_touch_ack_);
@@ skipping 203 matching lines @@
     if (ack_result == INPUT_EVENT_ACK_STATE_CONSUMED)
       send_touch_events_async_ = false;
     has_handler_for_current_sequence_ |=
         ack_result != INPUT_EVENT_ACK_STATE_NO_CONSUMER_EXISTS;
   } else if (WebTouchEventTraits::IsTouchSequenceEnd(event)) {
     has_handler_for_current_sequence_ = false;
   }
 }
 
 }  // namespace content