Change FocusSynchronizer to maintain active focus client and window.

ui/aura/mus/focus_synchronizer.h

Index: ui/aura/mus/focus_synchronizer.h
diff --git a/ui/aura/mus/focus_synchronizer.h b/ui/aura/mus/focus_synchronizer.h
index db2556d76155f0e1cdb8000f5a0ab6af217f901a..cca9ebaf2e7a0a78b7ddd445f3f40f5c230e89b7 100644
--- a/ui/aura/mus/focus_synchronizer.h
+++ b/ui/aura/mus/focus_synchronizer.h
@@ -6,8 +6,11 @@
 #define UI_AURA_MUS_FOCUS_SYNCHRONIZER_H_
 
 #include "base/macros.h"
+#include "base/observer_list.h"
+#include "ui/aura/aura_export.h"
 #include "ui/aura/client/focus_change_observer.h"
-#include "ui/aura/env_observer.h"
+#include "ui/aura/mus/focus_synchronizer_observer.h"
+#include "ui/aura/window_observer.h"
 
 namespace ui {
 namespace mojom {
@@ -26,42 +29,67 @@ class FocusClient;
 
 // FocusSynchronizer is resonsible for keeping focus in sync between aura
 // and the mus server.
-class FocusSynchronizer : public client::FocusChangeObserver,
-                          public EnvObserver {
+class AURA_EXPORT FocusSynchronizer : public client::FocusChangeObserver,
+                                      public WindowObserver {
  public:
   FocusSynchronizer(FocusSynchronizerDelegate* delegate,
                     ui::mojom::WindowTree* window_tree);
   ~FocusSynchronizer() override;
 
+  client::FocusClient* active_focus_client() { return active_focus_client_; }
+  Window* active_focus_client_root() { return active_focus_client_root_; }
+  WindowMus* focused_window() { return focused_window_; }
+
+  // Add and remove observers to the FocusSynchronizer to get notified when the
+  // |active_focus_client_| and the |active_focus_client_root_| change.
+  void AddObserver(FocusSynchronizerObserver* observer);
+  void RemoveObserver(FocusSynchronizerObserver* observer);
+
   // Called when the server side wants to change focus to |window|.
   void SetFocusFromServer(WindowMus* window);
 
   // Called when the focused window is destroyed.
   void OnFocusedWindowDestroyed();
 
-  WindowMus* focused_window() { return focused_window_; }
+  // Sets the active FocusClient and the window the FocusClient is associated
+  // with. |focus_client_root| is not necessarily the window that actually has
+  // focus.
+  void SetActiveFocusClient(client::FocusClient* focus_client,
+                            Window* focus_client_root);
 
  private:
-  void SetActiveFocusClient(client::FocusClient* focus_client);
+  // Called internally to set |active_focus_client_| and update observer.
+  void SetActiveFocusClientInternal(client::FocusClient* focus_client);
 
   // Called internally to set |focused_window_| and update the server.
   void SetFocusedWindow(WindowMus* window);
 
-  // Overriden from client::FocusChangeObserver:
+  // Called internally when notified that |active_focus_client_| and
+  // |active_focus_client_root_| have been changed.
+  void OnActiveFocusClientChanged(client::FocusClient* focus_client,
+                                  Window* focus_client_root);
+
+  // client::FocusChangeObserver:
   void OnWindowFocused(Window* gained_focus, Window* lost_focus) override;
 
-  // Overrided from EnvObserver:
-  void OnWindowInitialized(Window* window) override;
-  void OnActiveFocusClientChanged(client::FocusClient* focus_client,
-                                  Window* window) override;
+  // WindowObserver:
+  void OnWindowDestroying(Window* window) override;
+  void OnWindowPropertyChanged(Window* window,
+                               const void* key,
+                               intptr_t old) override;
 
   FocusSynchronizerDelegate* delegate_;
   ui::mojom::WindowTree* window_tree_;
 
-  client::FocusClient* active_focus_client_ = nullptr;
+  base::ObserverList<FocusSynchronizerObserver> observers_;
 
   bool setting_focus_ = false;
   WindowMus* window_setting_focus_to_ = nullptr;
+
+  client::FocusClient* active_focus_client_ = nullptr;
+  // The window that |active_focus_client_| is associated with.
+  Window* active_focus_client_root_ = nullptr;
+  // The window that actually has focus.
   WindowMus* focused_window_ = nullptr;
 
   DISALLOW_COPY_AND_ASSIGN(FocusSynchronizer);