[Blink] [PowerProfiler] Support accuracy level attribute for power data provider.

Source/devtools/front_end/sdk/PowerProfiler.js

 // 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.
 
 /**
  * @constructor
  * @extends {WebInspector.Object}
  */
 WebInspector.PowerProfiler = function()
 {
     WebInspector.Object.call(this);
     this._dispatcher = new WebInspector.PowerDispatcher(this);
+    PowerAgent.getAccuracyLevel(this._onAccuracyLevel.bind(this));
 }
 
 WebInspector.PowerProfiler.EventTypes = {
     PowerEventRecorded: "PowerEventRecorded"
 }
 
 WebInspector.PowerProfiler.prototype = {
 
     startProfile: function ()
     {
         PowerAgent.start();
     },
 
     stopProfile: function ()
     {
         PowerAgent.end();
     },
 
+    getAccuracyLevel: function()
+    {
+        return this._accuracyLevel;
+    },
+
+    _onAccuracyLevel: function(error, result) {
+        this._accuracyLevel = "";
+        if (error) {
+            console.log("Unable to retrieve PowerProfiler accuracy level: " + error);
+            return;
+        }
+        this._accuracyLevel = result;
+    },
+
     __proto__: WebInspector.Object.prototype
 }
 
 /**
  * @constructor
  * @implements {PowerAgent.Dispatcher}
  */
 WebInspector.PowerDispatcher = function(profiler)
 {
     this._profiler = profiler;
     InspectorBackend.registerPowerDispatcher(this);
 }
 
 WebInspector.PowerDispatcher.prototype = {
     dataAvailable: function(events)
     {
         for (var i = 0; i < events.length; ++i)
             this._profiler.dispatchEventToListeners(WebInspector.PowerProfiler.EventTypes.PowerEventRecorded, events[i]);
     }
 }
 
 /**
  * @type {!WebInspector.PowerProfiler}
  */
 WebInspector.powerProfiler;