Change FocusSynchronizer to maintain active focus client and window.

ui/aura/mus/window_tree_client.h

 // Copyright 2014 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_AURA_MUS_WINDOW_TREE_CLIENT_H_
 #define UI_AURA_MUS_WINDOW_TREE_CLIENT_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 101 matching lines @@
   void ConnectViaWindowTreeFactory();
 
   // Establishes the connection by way of WindowManagerWindowTreeFactory.
   void ConnectAsWindowManager();
 
   service_manager::Connector* connector() { return connector_; }
   ui::Gpu* gpu() { return gpu_.get(); }
   CaptureSynchronizer* capture_synchronizer() {
     return capture_synchronizer_.get();
   }
+  FocusSynchronizer* focus_synchronizer() { return focus_synchronizer_.get(); }
 
   bool connected() const { return tree_ != nullptr; }
   ClientSpecificId client_id() const { return client_id_; }
 
   void SetCanFocus(Window* window, bool can_focus);
   void SetCanAcceptDrops(WindowMus* window, bool can_accept_drops);
   void SetEventTargetingPolicy(WindowMus* window,
                                ui::mojom::EventTargetingPolicy policy);
   void SetPredefinedCursor(WindowMus* window,
                            ui::mojom::Cursor old_cursor,
@@ skipping 448 matching lines @@
   // ContextFactory that was set on Env originally.
   ui::ContextFactory* initial_context_factory_ = nullptr;
   base::WeakPtrFactory<WindowTreeClient> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowTreeClient);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_MUS_WINDOW_TREE_CLIENT_H_