chromeos: makes it possible for windows to outlive WindowTreeClient

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 616 matching lines @@
   bool got_initial_displays_ = false;
 
   // Set to true if the next CompositorFrame will block on a new child surface.
   bool synchronizing_with_child_on_next_frame_ = false;
 
   // Set to true if this WindowTreeClient is currently holding pointer moves.
   bool holding_pointer_moves_ = false;
 
   gfx::Insets normal_client_area_insets_;
 
+  bool in_shutdown_ = false;
+
   base::WeakPtrFactory<WindowTreeClient> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowTreeClient);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_MUS_WINDOW_TREE_CLIENT_H_