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

ash/touch/touch_uma.h

Index: ash/touch/touch_uma.h
diff --git a/ash/touch/touch_uma.h b/ash/touch/touch_uma.h
index 7af520453ef57166af23fb98e4501195497490d6..371b80bfce769db2c9d2d5b616136f5e202fa4cb 100644
--- a/ash/touch/touch_uma.h
+++ b/ash/touch/touch_uma.h
@@ -75,7 +75,7 @@ class ASH_EXPORT TouchUMA {
   // 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);
 };