Store the id of a contributing motion event in GestureEventData

ui/events/gesture_detection/gesture_event_data.h

 // Copyright 2014 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_GESTURE_DETECTION_GESTURE_EVENT_DATA_H_
 #define UI_EVENTS_GESTURE_DETECTION_GESTURE_EVENT_DATA_H_
 
 #include "base/time/time.h"
 #include "ui/events/event_constants.h"
 #include "ui/events/gesture_detection/gesture_detection_export.h"
 #include "ui/events/gesture_event_details.h"
 
 namespace ui {
 
 class GestureEventDataPacket;
 
 struct GESTURE_DETECTION_EXPORT GestureEventData {
   GestureEventData(EventType type,
+                   int motion_event_id,
                    base::TimeTicks time,
                    float x,
                    float y,
                    const GestureEventDetails& details);
 
   GestureEventData(EventType type,
+                   int motion_event_id,
                    base::TimeTicks time,
                    float x,
                    float y);
 
   EventType type;
+  int motion_event_id;
   base::TimeTicks time;
   float x;
   float y;
 
   GestureEventDetails details;
 
  private:
   friend class GestureEventDataPacket;
 
   // Initializes type to GESTURE_TYPE_INVALID.
   GestureEventData();
 };
 
 }  //  namespace ui
 
 #endif  // UI_EVENTS_GESTURE_DETECTION_GESTURE_EVENT_DATA_H_