Coalesce async touch move events until the ack back from render

content/common/input/synthetic_web_input_event_builders.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/common/input/synthetic_web_input_event_builders.h"
 
 #include "base/logging.h"
 #include "content/common/input/web_touch_event_traits.h"
 #include "ui/events/base_event_utils.h"
 #include "ui/events/keycodes/keyboard_codes.h"
@@ skipping 150 matching lines @@
     if (touches[i].state == WebTouchPoint::StateReleased)
       continue;
 
     touches[point] = touches[i];
     touches[point].state = WebTouchPoint::StateStationary;
     ++point;
   }
   touchesLength = point;
   type = WebInputEvent::Undefined;
   causesScrollingIfUncanceled = false;
+  uniqueTouchEventId = ui::GetNextTouchEventId();
 }
 
 int SyntheticWebTouchEvent::PressPoint(float x, float y) {
   if (touchesLength == touchesLengthCap)
     return -1;
   WebTouchPoint& point = touches[touchesLength];
   point.id = touchesLength;
   point.position.x = point.screenPosition.x = x;
   point.position.y = point.screenPosition.y = y;
   point.state = WebTouchPoint::StatePressed;
@@ skipping 34 matching lines @@
   touches[index].state = WebTouchPoint::StateCancelled;
   WebTouchEventTraits::ResetType(
       WebInputEvent::TouchCancel, timeStampSeconds, this);
 }
 
 void SyntheticWebTouchEvent::SetTimestamp(base::TimeDelta timestamp) {
   timeStampSeconds = timestamp.InSecondsF();
 }
 
 }  // namespace content