exo: WMHelperMus: Add focus and activation support.

components/exo/wm_helper_mus.h

 // Copyright 2016 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 COMPONENTS_EXO_WM_HELPER_MUS_H_
 #define COMPONENTS_EXO_WM_HELPER_MUS_H_
 
 #include "base/macros.h"
 #include "components/exo/wm_helper.h"
+#include "services/ui/public/cpp/window_tree_client_observer.h"
+#include "ui/aura/client/focus_change_observer.h"
 
 namespace exo {
 
 // A helper class for accessing WindowManager related features.
-class WMHelperMus : public WMHelper {
+class WMHelperMus : public WMHelper,
+                    public ui::WindowTreeClientObserver,
+                    public aura::client::FocusChangeObserver {
  public:
   WMHelperMus();
   ~WMHelperMus() override;
 
   // Overriden from WMHelper:
   const ash::DisplayInfo GetDisplayInfo(int64_t display_id) const override;
   aura::Window* GetContainer(int container_id) override;
   aura::Window* GetActiveWindow() const override;
   aura::Window* GetFocusedWindow() const override;
   ui::CursorSetType GetCursorSet() const override;
   void AddPreTargetHandler(ui::EventHandler* handler) override;
   void PrependPreTargetHandler(ui::EventHandler* handler) override;
   void RemovePreTargetHandler(ui::EventHandler* handler) override;
   void AddPostTargetHandler(ui::EventHandler* handler) override;
   void RemovePostTargetHandler(ui::EventHandler* handler) override;
   bool IsMaximizeModeWindowManagerEnabled() const override;
 
+  // Overriden from ui::WindowTreeClientObserver:
+  void OnWindowTreeFocusChanged(ui::Window* gained_focus,
+                                ui::Window* lost_focus) override;
+
+  // Overriden from ui::client::FocusChangeObserver:
+  void OnWindowFocused(aura::Window* gained_focus,
+                       aura::Window* lost_focus) override;
+
  private:
+  aura::Window* active_window_;
+  aura::Window* focused_window_;
+
   DISALLOW_COPY_AND_ASSIGN(WMHelperMus);
 };
 
 }  // namespace exo
 
 #endif  // COMPONENTS_EXO_WM_HELPER_H_