Converts WmActivationObserver to aura::client::ActivationChangeObserver

ash/common/wm/mru_window_tracker.h

Index: ash/common/wm/mru_window_tracker.h
diff --git a/ash/common/wm/mru_window_tracker.h b/ash/common/wm/mru_window_tracker.h
index 1c820e398fc7e9ec9ffeee2a420916b995f47ee5..595c04f4d5ff5e093cf2a57821f16d3118b5083f 100644
--- a/ash/common/wm/mru_window_tracker.h
+++ b/ash/common/wm/mru_window_tracker.h
@@ -9,9 +9,9 @@
 #include <vector>
 
 #include "ash/ash_export.h"
-#include "ash/common/wm_activation_observer.h"
 #include "base/macros.h"
 #include "ui/aura/window_observer.h"
+#include "ui/wm/public/activation_change_observer.h"
 
 namespace ash {
 
@@ -19,8 +19,9 @@ class WmWindow;
 
 // Maintains a most recently used list of windows. This is used for window
 // cycling using Alt+Tab and overview mode.
-class ASH_EXPORT MruWindowTracker : public WmActivationObserver,
-                                    public aura::WindowObserver {
+class ASH_EXPORT MruWindowTracker
+    : public aura::client::ActivationChangeObserver,
+      public aura::WindowObserver {
  public:
   using WindowList = std::vector<WmWindow*>;
 
@@ -47,9 +48,10 @@ class ASH_EXPORT MruWindowTracker : public WmActivationObserver,
   // front.
   void SetActiveWindow(WmWindow* active_window);
 
-  // Overridden from WmActivationObserver:
-  void OnWindowActivated(WmWindow* gained_active,
-                         WmWindow* lost_active) override;
+  // Overridden from aura::client::ActivationChangeObserver:
+  void OnWindowActivated(ActivationReason reason,
+                         aura::Window* gained_active,
+                         aura::Window* lost_active) override;
 
   // Overridden from aura::WindowObserver:
   void OnWindowDestroyed(aura::Window* window) override;