Added UMA statistics for changing the active window via click or touch events.

ash/wm/mru_window_tracker.h

Index: ash/wm/mru_window_tracker.h
diff --git a/ash/wm/mru_window_tracker.h b/ash/wm/mru_window_tracker.h
index f32f708a3a210cd5549f89561897e1d38c8e12e7..06673a83419d1c0150d0efb655c1f54c667883cb 100644
--- a/ash/wm/mru_window_tracker.h
+++ b/ash/wm/mru_window_tracker.h
@@ -65,8 +65,10 @@ class ASH_EXPORT MruWindowTracker
   void SetActiveWindow(aura::Window* active_window);
 
   // Overridden from aura::client::ActivationChangeObserver:
-  void OnWindowActivated(aura::Window* gained_active,
-                         aura::Window* lost_active) override;
+  void OnWindowActivated(
+      aura::client::ActivationChangeObserver::ActivationReason reason,
+      aura::Window* gained_active,
+      aura::Window* lost_active) override;
 
   // Overridden from WindowObserver:
   void OnWindowDestroyed(aura::Window* window) override;