Add setBatteryListener into Platform.

public/platform/WebBatteryListener.h

Index: public/platform/WebBatteryListener.h
diff --git a/public/platform/WebBatteryListener.h b/public/platform/WebBatteryListener.h
deleted file mode 100644
index b69814adeef7140746471461bbc40e78791d1b5a..0000000000000000000000000000000000000000
--- a/public/platform/WebBatteryListener.h
+++ /dev/null
@@ -1,24 +0,0 @@
-// 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 WebBatteryListener_h
-#define WebBatteryListener_h
-
-#include "WebBatteryStatus.h"
-
-namespace blink {
-
-class WebBatteryStatus;
-
-class WebBatteryListener {
-public:
-    // This method is called when a new battery status is available.
-    virtual void updateBatteryStatus(const WebBatteryStatus&) = 0;
-
-    virtual ~WebBatteryListener() { }
-};
-
-} // namespace blink
-
-#endif // WebBatteryListener_h