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

ui/wm/public/activation_change_observer.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_WM_PUBLIC_ACTIVATION_CHANGE_OBSERVER_H_
 #define UI_WM_PUBLIC_ACTIVATION_CHANGE_OBSERVER_H_
 
 #include "ui/aura/aura_export.h"
 
 namespace aura {
 class Window;
 
 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
   // selected for activation. This can happen when a window requested for
   // activation cannot be activated because a system modal window is active.
   virtual void OnAttemptToReactivateWindow(aura::Window* request_active,
                                            aura::Window* actual_active) {}
 
  protected:
   virtual ~ActivationChangeObserver() {}
 };
 
 // Gets/Sets the ActivationChangeObserver for a specific window. This observer
 // is notified after the ActivationClient notifies all registered observers.
 AURA_EXPORT void SetActivationChangeObserver(
     Window* window,
     ActivationChangeObserver* observer);
 AURA_EXPORT ActivationChangeObserver* GetActivationChangeObserver(
     Window* window);
 
 }  // namespace client
 }  // namespace aura
 
 #endif  // UI_WM_PUBLIC_ACTIVATION_CHANGE_OBSERVER_H_