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

ash/touch/touch_hud_debug.cc

Index: ash/touch/touch_hud_debug.cc
diff --git a/ash/touch/touch_hud_debug.cc b/ash/touch/touch_hud_debug.cc
index 57b96560195ee0c2c32c848ec78d3ffb646e5eaa..4bd76a551edf4f7b35eb69650ef8e10c8362c832 100644
--- a/ash/touch/touch_hud_debug.cc
+++ b/ash/touch/touch_hud_debug.cc
@@ -96,7 +96,7 @@ struct TouchPointLog {
       : id(touch.touch_id()),
         type(touch.type()),
         location(touch.root_location()),
-        timestamp(touch.time_stamp().InMillisecondsF()),
+        timestamp((touch.time_stamp() - base::TimeTicks()).InMillisecondsF()),

[majidvp, 2016/05/16 12:49:50]

This is the pattern I use when it is needed to convert a TimeTicks to TimeDelta:
delta = ticks - base::TimeTicks()

There are a few of such cases where a conversion is needed. 
Few of them are artifact of |MenuRunner::closing_event_time()| being a delta
which
should get fixed in a separate patch.

         radius_x(touch.pointer_details().radius_x),
         radius_y(touch.pointer_details().radius_y),
         pressure(touch.pointer_details().force),