mash: Migrate ScopedTargetRootWindow to //ash/common

ash/common/scoped_root_window_for_new_windows.h

+// 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_COMMON_SCOPED_ROOT_WINDOW_FOR_NEW_WINDOWS_H_
+#define ASH_COMMON_SCOPED_ROOT_WINDOW_FOR_NEW_WINDOWS_H_
+
+#include "ash/ash_export.h"
+
+namespace ash {
+
+// Allows a temporary override of the root window where new windows get created.
+// An example usage is to specify the target root window when creating a new
+// window by clicking on a shelf icon.
+class ASH_EXPORT ScopedRootWindowForNewWindows {

[msw, 2016/08/01 21:36:15]

q: Could this just be a typedef for base::AutoReset<WmWindow>?

+ public:
+  virtual ~ScopedRootWindowForNewWindows() {}
+};
+
+}  // namespace ash
+
+#endif  // ASH_COMMON_SCOPED_ROOT_WINDOW_FOR_NEW_WINDOWS_H_