Intorduce PowerButtonObserver API

athena/input/public/input_manager.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_INPUT_PUBLIC_INPUT_MANAGER_H_
 #define ATHENA_INPUT_PUBLIC_INPUT_MANAGER_H_
 
 #include "athena/athena_export.h"
 
 namespace aura {
 class Window;
 }
 
 namespace ui {
 class EventTarget;
 }
 
 namespace athena {
 class AcceleratorManager;
 
+class PowerButtonObserver {
+ public:
+  enum State {
+    PRESSED,
+    LONG_PRESSED,
+    RELEASED,
+  };
+
+  virtual void OnPowerButtonStateChanged(State state) = 0;
+};
+
 class ATHENA_EXPORT InputManager {
  public:
   // Creates and deletes the singleton object of the InputManager
   // implementation.
   static InputManager* Create();
   static InputManager* Get();
   static void Shutdown();
 
   // TODO(oshima): Fix the initialization process and replace this
   // with EnvObserver::WindowInitialized
   virtual void OnRootWindowCreated(aura::Window* root_window) = 0;
 
+  // Add/remove power button observer.
+  virtual void AddPowerButtonObserver(PowerButtonObserver* observer) = 0;
+  virtual void RemovePowerButtonObserver(PowerButtonObserver* observer) = 0;
+
   virtual ui::EventTarget* GetTopmostEventTarget() = 0;
   virtual AcceleratorManager* GetAcceleratorManager() = 0;
 
   virtual ~InputManager() {}
 };
 
 }  // namespace athena
 
 #endif  // ATHENA_INPUT_PUBLIC_INPUT_MANAGER_H_