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

ash/keyboard_uma_event_filter.cc

Index: ash/keyboard_uma_event_filter.cc
diff --git a/ash/keyboard_uma_event_filter.cc b/ash/keyboard_uma_event_filter.cc
index f3864bf033f2fb3b27163d494222cf935565353c..12c9d69ac2c40756ead50c69bde771c2d082bbc1 100644
--- a/ash/keyboard_uma_event_filter.cc
+++ b/ash/keyboard_uma_event_filter.cc
@@ -30,7 +30,7 @@ void KeyboardUMAEventFilter::OnKeyEvent(ui::KeyEvent* event) {
 
   // Reset the timer on non-character keystrokes.
   if (!isprint(event->GetCharacter())) {
-    last_keystroke_time_ = base::TimeDelta();
+    last_keystroke_time_ = base::TimeTicks();
     return;
   }