Revert of 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 04682e84e9cd9306ad6a20e07737b4e17f144f3d..cc7017530f98ee41d6cf1ea00fedf1620d0f4619 100644
--- a/athena/input/public/input_manager.h
+++ b/athena/input/public/input_manager.h
@@ -18,17 +18,6 @@
 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
@@ -41,10 +30,6 @@
   // 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;