Change ui::Event::time_stamp from TimeDelta to TimeTicks

ash/touch/touch_uma.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 ASH_TOUCH_TOUCH_OBSERVER_UMA_H_
 #define ASH_TOUCH_TOUCH_OBSERVER_UMA_H_
 
 #include <map>
 
 #include "ash/shell.h"
@@ skipping 57 matching lines @@
 
   void UpdateTouchState(const ui::TouchEvent& event);
   GestureActionType FindGestureActionType(aura::Window* window,
                                           const ui::GestureEvent& event);
 
   bool is_single_finger_gesture_;
   // These are used to measure the number of touch-start events we receive in a
   // quick succession, regardless of the target window.
   bool touch_in_progress_;
   int burst_length_;
-  base::TimeDelta last_touch_down_time_;
+  base::TimeTicks last_touch_down_time_;
 
   DISALLOW_COPY_AND_ASSIGN(TouchUMA);
 };
 
 }  // namespace ash
 
 #endif  // ASH_TOUCH_TOUCH_OBSERVER_UMA_H_