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

ui/wm/public/activation_change_observer.h

Index: ui/wm/public/activation_change_observer.h
diff --git a/ui/wm/public/activation_change_observer.h b/ui/wm/public/activation_change_observer.h
index 68d5b8a742acedbc5c99bd19867bb41d67f63a17..930f12f8679d646e8f0443192e0c954bda888004 100644
--- a/ui/wm/public/activation_change_observer.h
+++ b/ui/wm/public/activation_change_observer.h
@@ -14,11 +14,23 @@ namespace client {
 
 class AURA_EXPORT ActivationChangeObserver {
  public:
+  // The reason or cause of a window activation change.
+  enum class ActivationReason {
+    // When a window is activated due to a call to the ActivationClient API.
+    kActivationClient,

[sky, 2015/06/02 15:43:03]

In chrome we don't use this style for enums, we use ALL_CAPS. See chrome style
guide for specifics.

[bruthig, 2015/06/03 21:59:31]

Done.

+    // When a user clicks or taps a window in the 2-dimensional screen space.
+    kInputEvent,
+    // When a new window is activated as a side effect of a window
+    // disposition changing.
+    kWindowDispositionChanged,
+  };
+
   // Called when |active| gains focus, or there is no active window
   // (|active| is NULL in this case.) |old_active| refers to the
   // previous active window or NULL if there was no previously active
-  // window.
-  virtual void OnWindowActivated(Window* gained_active,
+  // window. |reason| specifies the cause of the activation change.
+  virtual void OnWindowActivated(ActivationReason reason,
+                                 Window* gained_active,
                                  Window* lost_active) = 0;
 
   // Called when during window activation the currently active window is