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_