Relocate and refactor overview mode files.

ash/wm/window_selector_delegate.h

-// Copyright 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 ASH_WM_WINDOW_SELECTOR_DELEGATE_H_
-#define ASH_WM_WINDOW_SELECTOR_DELEGATE_H_
-
-#include "ash/ash_export.h"
-#include "base/compiler_specific.h"
-
-namespace aura {
-class Window;
-}
-
-namespace ash {
-
-// Implement this class to handle the selection event from WindowSelector.
-class ASH_EXPORT WindowSelectorDelegate {
- public:
-  // Invoked when a window is selected.
-  virtual void OnWindowSelected(aura::Window* window) = 0;
-
-  // Invoked if selection is canceled.
-  virtual void OnSelectionCanceled() = 0;
-
- protected:
-  virtual ~WindowSelectorDelegate() {}
-};
-
-}  // namespace ash
-
-#endif  // ASH_WM_WINDOW_SELECTOR_DELEGATE_H_