Add support to Battery Status API in blink.

Source/modules/battery/BatteryManager.idl

Index: Source/modules/battery/BatteryManager.idl
diff --git a/Source/modules/battery/BatteryManager.idl b/Source/modules/battery/BatteryManager.idl
new file mode 100644
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+++ b/Source/modules/battery/BatteryManager.idl
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+// 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.
+
+// http://dev.w3.org/2009/dap/system-info/battery-status.html
+[
+    NoInterfaceObject,
+    RuntimeEnabled=BatteryStatus,
+] interface BatteryManager : EventTarget {
+    readonly attribute boolean charging;
+    readonly attribute double chargingTime;
+    readonly attribute double dischargingTime;
+    readonly attribute double level;
+
+    attribute EventHandler onchargingchange;
+    attribute EventHandler onchargingtimechange;
+    attribute EventHandler ondischargingtimechange;
+    attribute EventHandler onlevelchange;
+
+};
+