Adds WmWindow and converts WindowState to use it

ash/wm/window_state_aura.h

Index: ash/wm/window_state_aura.h
diff --git a/ash/wm/window_state_aura.h b/ash/wm/window_state_aura.h
new file mode 100644
index 0000000000000000000000000000000000000000..6d6b122e9a17cd4099f6bf68cc2f2cb91e599be0
--- /dev/null
+++ b/ash/wm/window_state_aura.h
@@ -0,0 +1,33 @@
+// Copyright 2016 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 ASH_WM_WINDOW_STATE_AURA_H_
+#define ASH_WM_WINDOW_STATE_AURA_H_
+
+#include "ash/ash_export.h"
+
+namespace aura {
+class Window;
+}
+
+namespace ash {
+namespace wm {
+
+class WindowState;
+
+// Returns the WindowState for active window. Returns |NULL|
+// if there is no active window.
+ASH_EXPORT WindowState* GetActiveWindowState();
+
+// Returns the WindowState for |window|. Creates WindowState
+// if it didn't exist. The settings object is owned by |window|.
+ASH_EXPORT WindowState* GetWindowState(aura::Window* window);
+
+// const version of GetWindowState.
+ASH_EXPORT const WindowState* GetWindowState(const aura::Window* window);
+
+}  // namespace wm
+}  // namespace ash
+
+#endif  // ASH_WM_WINDOW_STATE_AURA_H_