Set the unique_event_id when converting from TouchEvent to WebTouchEvent

ui/events/gesture_detection/motion_event.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_MOTION_EVENT_H_
 #define UI_EVENTS_GESTURE_DETECTION_MOTION_EVENT_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "base/time/time.h"
 #include "ui/events/gesture_detection/gesture_detection_export.h"
@@ skipping 28 matching lines @@
     BUTTON_BACK = 1 << 3,
     BUTTON_FORWARD = 1 << 4,
   };
 
   // The implementer promises that |GetPointerId()| will never exceed
   // MAX_POINTER_ID.
   enum { MAX_POINTER_ID = 31, MAX_TOUCH_POINT_COUNT = 16 };
 
   virtual ~MotionEvent() {}
 
-  virtual int GetId() const = 0;
+
+  // An unique identifier this motion event.
+  virtual uint64 GetUniqueEventId() const = 0;
   virtual Action GetAction() const = 0;
   // Only valid if |GetAction()| returns ACTION_POINTER_UP or
   // ACTION_POINTER_DOWN.
   virtual int GetActionIndex() const = 0;
   virtual size_t GetPointerCount() const = 0;
   virtual int GetPointerId(size_t pointer_index) const = 0;
   virtual float GetX(size_t pointer_index) const = 0;
   virtual float GetY(size_t pointer_index) const = 0;
   virtual float GetRawX(size_t pointer_index) const = 0;
   virtual float GetRawY(size_t pointer_index) const = 0;
@@ skipping 13 matching lines @@
                                         size_t historical_index) const;
   virtual float GetHistoricalX(size_t pointer_index,
                                size_t historical_index) const;
   virtual float GetHistoricalY(size_t pointer_index,
                                size_t historical_index) const;
 
   // Get the id of the device which created the event. Currently Aura only.
   virtual int GetSourceDeviceId(size_t pointer_index) const;
 
   // Utility accessor methods for convenience.
+  int GetPointerId() const { return GetPointerId(0); }
   float GetX() const { return GetX(0); }
   float GetY() const { return GetY(0); }
   float GetRawX() const { return GetRawX(0); }
   float GetRawY() const { return GetRawY(0); }
   float GetRawOffsetX() const { return GetRawX() - GetX(); }
   float GetRawOffsetY() const { return GetRawY() - GetY(); }
 
   float GetTouchMajor() const { return GetTouchMajor(0); }
   float GetTouchMinor() const { return GetTouchMinor(0); }
 
   // Returns the orientation of the major axis clockwise from vertical, in
   // radians. The return value lies in [-PI/2, PI/2].
   float GetOrientation() const { return GetOrientation(0); }
 
   float GetPressure() const { return GetPressure(0); }
   ToolType GetToolType() const { return GetToolType(0); }
 
   // O(N) search of pointers (use sparingly!). Returns -1 if |id| nonexistent.
   int FindPointerIndexOfId(int id) const;
 
   // Note that these methods perform shallow copies of the originating events.
   // They guarantee only that the returned type will reflect the same
   // data exposed by the MotionEvent interface; no guarantees are made that the
   // underlying implementation is identical to the source implementation.
   scoped_ptr<MotionEvent> Clone() const;

[jdduke (slow), 2015/04/17 20:30:01]

So what's the right thing to do if/when we Clone the event? Do we just copy the
unique id?

[lanwei, 2015/04/20 19:58:59]

We can just copy the unique_event_id when we clone the MotionEvent. 

   scoped_ptr<MotionEvent> Cancel() const;
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_GESTURE_DETECTION_MOTION_EVENT_H_