Adds views::corewm::WMState to install common state

ui/aura/client/window_stacking_client.h

 // Copyright (c) 2013 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_CLIENT_WINDOW_STACKING_CLIENT_H_
 #define UI_AURA_CLIENT_WINDOW_STACKING_CLIENT_H_
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "ui/aura/aura_export.h"
 #include "ui/aura/window.h"
 
 namespace aura {
 namespace client {
 
 class AURA_EXPORT WindowStackingClient {
  public:
-  virtual ~WindowStackingClient() {}
-
   // Invoked from the various Window stacking functions. Allows the
   // WindowStackingClient to alter the source, target and/or direction to stack.
-  virtual void AdjustStacking(Window** child,
+  // Returns true if stacking should continue; false if the stacking should not
+  // happen.
+  virtual bool AdjustStacking(Window** child,
                               Window** target,
                               Window::StackDirection* direction) = 0;
+
+ protected:
+  virtual ~WindowStackingClient() {}
 };
 
-// Sets/gets the WindowStackingClient. The setter takes ownership of |client|.
+// Sets/gets the WindowStackingClient. This does *not* take ownership of
+// |client|. It is assumed the caller will invoke SetWindowStackingClient(NULL)
+// before deleting |client|.
 AURA_EXPORT void SetWindowStackingClient(WindowStackingClient* client);
 AURA_EXPORT WindowStackingClient* GetWindowStackingClient();
 
 }  // namespace client
 }  // namespace aura
 
 #endif  // UI_AURA_CLIENT_WINDOW_STACKING_CLIENT_H_