Intorduce PowerButtonObserver API

athena/input/public/input_manager.h

Index: athena/input/public/input_manager.h
diff --git a/athena/input/public/input_manager.h b/athena/input/public/input_manager.h
index cc7017530f98ee41d6cf1ea00fedf1620d0f4619..04682e84e9cd9306ad6a20e07737b4e17f144f3d 100644
--- a/athena/input/public/input_manager.h
+++ b/athena/input/public/input_manager.h
@@ -18,6 +18,17 @@ 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
@@ -30,6 +41,10 @@ class ATHENA_EXPORT InputManager {
   // 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;