Coalesce async touch move events until the ack back from render

ui/events/event.h

 // Copyright (c) 2012 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.
 
 #ifndef UI_EVENTS_EVENT_H_
 #define UI_EVENTS_EVENT_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/event_types.h"
@@ skipping 500 matching lines @@
              float angle,
              float force);
 
   TouchEvent(const TouchEvent& copy);
 
   ~TouchEvent() override;
 
   // The id of the pointer this event modifies.
   int touch_id() const { return touch_id_; }
   // A unique identifier for this event.
-  uint64 unique_event_id() const { return unique_event_id_; }
+  uint32 unique_event_id() const { return unique_event_id_; }
   // If we aren't provided with a radius on one axis, use the
   // information from the other axis.
   float radius_x() const { return radius_x_ > 0 ? radius_x_ : radius_y_; }
   float radius_y() const { return radius_y_ > 0 ? radius_y_ : radius_x_; }
   float rotation_angle() const { return rotation_angle_; }
   float force() const { return force_; }
 
   void set_may_cause_scrolling(bool causes) { may_cause_scrolling_ = causes; }
   bool may_cause_scrolling() const { return may_cause_scrolling_; }
 
@@ skipping 19 matching lines @@
 
  private:
   // Adjusts rotation_angle_ to within the acceptable range.
   void FixRotationAngle();
 
   // The identity (typically finger) of the touch starting at 0 and incrementing
   // for each separable additional touch that the hardware can detect.
   const int touch_id_;
 
   // A unique identifier for the touch event.
-  const uint64 unique_event_id_;
+  const uint32 unique_event_id_;
 
   // Radius of the X (major) axis of the touch ellipse. 0.0 if unknown.
   float radius_x_;
 
   // Radius of the Y (minor) axis of the touch ellipse. 0.0 if unknown.
   float radius_y_;
 
   // Clockwise angle (in degrees) of the major axis from the X axis. Must be
   // less than 180 and non-negative.
   float rotation_angle_;
@@ skipping 307 matching lines @@
 
   const GestureEventDetails& details() const { return details_; }
 
  private:
   GestureEventDetails details_;
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_EVENT_H_