Add setBatteryListener into Platform.

Source/modules/battery/BatteryDispatcher.cpp

 // 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.
 
 #include "config.h"
 #include "modules/battery/BatteryDispatcher.h"
 
 #include "core/events/Event.h"
 #include "modules/battery/BatteryStatus.h"
 #include "platform/NotImplemented.h"
@@ skipping 67 matching lines @@
                 static_cast<BatteryManager*>(m_controllers[i])->didChangeBatteryStatus(event);
         }
     }
 
     if (m_needsPurge)
         purgeControllers();
 }
 
 void BatteryDispatcher::startListening()
 {
-    notImplemented();
+    blink::Platform::current()->setBatteryStatusListener(this);
 }
 
 void BatteryDispatcher::stopListening()
 {
-    notImplemented();
+    blink::Platform::current()->setBatteryStatusListener(0);
 }
 
 }