Revert of athena: Add a minimized state for the home-card.

athena/wm/public/window_manager_observer.h

-// Copyright 2014 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 ATHENA_SCREEN_PUBLIC_WINDOW_MANAGER_OBSERVER_H_
-#define ATHENA_SCREEN_PUBLIC_WINDOW_MANAGER_OBSERVER_H_
-
-#include "athena/athena_export.h"
-
-namespace athena {
-
-class ATHENA_EXPORT WindowManagerObserver {
- public:
-  virtual ~WindowManagerObserver() {}
-
-  // Called when the overview mode is displayed.
-  virtual void OnOverviewModeEnter() = 0;
-
-  // Called when going out of overview mode.
-  virtual void OnOverviewModeExit() = 0;
-};
-
-}  // namespace athena
-
-#endif  // ATHENA_SCREEN_PUBLIC_WINDOW_MANAGER_OBSERVER_H_