Change FocusSynchronizer to maintain active focus client and window.

ui/aura/mus/window_tree_client.cc

 // 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.
 
 #include "ui/aura/mus/window_tree_client.h"
 
 #include <stddef.h>
 
 #include <string>
 #include <utility>
@@ skipping 600 matching lines @@
         transport_value ? std::move(*transport_value) : std::vector<uint8_t>();
   }
 
   const uint32_t change_id = ScheduleInFlightChange(
       base::MakeUnique<CrashInFlightChange>(window, ChangeType::NEW_WINDOW));
   tree_->NewWindow(change_id, window->server_id(),
                    std::move(transport_properties));
 }
 
 void WindowTreeClient::OnWindowMusDestroyed(WindowMus* window, Origin origin) {
-  if (focus_synchronizer_->focused_window() == window)
+  if (WindowMus::Get(focus_synchronizer_->focused_window()) == window)
     focus_synchronizer_->OnFocusedWindowDestroyed();
 
   // TODO: decide how to deal with windows not owned by this client.
   if (origin == Origin::CLIENT &&
       (WasCreatedByThisClient(window) || IsRoot(window))) {
     const uint32_t change_id =
         ScheduleInFlightChange(base::MakeUnique<CrashInFlightChange>(
             window, ChangeType::DELETE_WINDOW));
     tree_->DeleteWindow(change_id, window->server_id());
   }
@@ skipping 1191 matching lines @@
   return ScheduleInFlightChange(base::MakeUnique<InFlightCaptureChange>(
       this, capture_synchronizer_.get(), window));
 }
 
 uint32_t WindowTreeClient::CreateChangeIdForFocus(WindowMus* window) {
   return ScheduleInFlightChange(base::MakeUnique<InFlightFocusChange>(
       this, focus_synchronizer_.get(), window));
 }
 
 }  // namespace aura