exo: WMHelperMus: Add focus and activation support.

components/exo/wm_helper_mus.h

Index: components/exo/wm_helper_mus.h
diff --git a/components/exo/wm_helper_mus.h b/components/exo/wm_helper_mus.h
index ea03df71de97afae787a732eb0a0211e8d17b868..6a6f6fe59ab89eea1cefad9b88aabd1bb28980ba 100644
--- a/components/exo/wm_helper_mus.h
+++ b/components/exo/wm_helper_mus.h
@@ -7,11 +7,15 @@
 
 #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;
@@ -29,7 +33,18 @@ class WMHelperMus : public WMHelper {
   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);
 };