Store the id of a contributing motion event in GestureEventData

content/browser/renderer_host/input/motion_event_web.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 CONTENT_BROWSER_RENDERER_HOST_INPUT_MOTION_EVENT_WEB_H_
 #define CONTENT_BROWSER_RENDERER_HOST_INPUT_MOTION_EVENT_WEB_H_
 
 #include "third_party/WebKit/public/web/WebInputEvent.h"
 #include "ui/events/gesture_detection/motion_event.h"
 
 namespace content {
 
 // Implementation of ui::MotionEvent wrapping a WebTouchEvent.
 class MotionEventWeb : public ui::MotionEvent {
  public:
   explicit MotionEventWeb(const blink::WebTouchEvent& event);
   virtual ~MotionEventWeb();
 
   // ui::MotionEvent
+  virtual int GetId() const OVERRIDE;
   virtual Action GetAction() const OVERRIDE;
   virtual int GetActionIndex() const OVERRIDE;
   virtual size_t GetPointerCount() const OVERRIDE;
   virtual int GetPointerId(size_t pointer_index) const OVERRIDE;
   virtual float GetX(size_t pointer_index) const OVERRIDE;
   virtual float GetY(size_t pointer_index) const OVERRIDE;
   virtual float GetTouchMajor(size_t pointer_index) const OVERRIDE;
   virtual float GetPressure(size_t pointer_index) const OVERRIDE;
   virtual base::TimeTicks GetEventTime() const OVERRIDE;
   virtual size_t GetHistorySize() const OVERRIDE;
@@ skipping 15 matching lines @@
   blink::WebTouchEvent event_;
   Action cached_action_;
   int cached_action_index_;
 
   DISALLOW_COPY_AND_ASSIGN(MotionEventWeb);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_INPUT_MOTION_EVENT_WEB_H_