Add window overview mode behind --ash-enable-overview-mode flag to F5 key.

ash/wm/window_selector_delegate.h

Index: ash/wm/window_selector_delegate.h
diff --git a/ash/wm/window_selector_delegate.h b/ash/wm/window_selector_delegate.h
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+++ b/ash/wm/window_selector_delegate.h
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+// 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 ASH_WM_WINDOW_SELECTOR_DELEGATE_H_
+#define ASH_WM_WINDOW_SELECTOR_DELEGATE_H_
+
+#include "base/compiler_specific.h"
+
+namespace aura {
+class Window;
+}
+
+namespace ash {
+
+// Implement this class to handle the selection event from WindowSelector.
+class 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_