Aura-Mus: Implement gutter in the embedder.

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 590 matching lines @@
   std::unique_ptr<discardable_memory::ClientDiscardableSharedMemoryManager>
       discardable_shared_memory_manager_;
 
   // If |compositor_context_factory_| is installed on Env, then this is the
   // ContextFactory that was set on Env originally.
   ui::ContextFactory* initial_context_factory_ = nullptr;
 
   // Set to true once OnWmDisplayAdded() is called.
   bool got_initial_displays_ = false;
 
+  gfx::Insets normal_client_area_insets_;
+
   base::WeakPtrFactory<WindowTreeClient> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowTreeClient);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_MUS_WINDOW_TREE_CLIENT_H_