DevTools: adopt FilmStripModel to new screenshot recorder trace format

Source/devtools/front_end/sdk/TracingModel.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
  * @param {!WebInspector.BackingStorage} backingStorage
  */
@@ skipping 670 matching lines @@
         console.error("Missing mandatory 'snapshot' argument at " + payload.ts / 1000);
         return snapshot;
     }
     if (payload.args)
         snapshot.addArgs(payload.args);
     return snapshot;
 }
 
 WebInspector.TracingModel.ObjectSnapshot.prototype = {
     /**
-     * @param {function(?Object)} callback
+     * @param {function(?)} callback
      */
     requestObject: function(callback)
     {
         var snapshot = this.args["snapshot"];
         if (snapshot) {
             callback(snapshot);
             return;
         }
         this._backingStorage().then(onRead, callback.bind(null, null));
         /**
          * @param {?string} result
          */
         function onRead(result)
         {
             if (!result) {
                 callback(null);
                 return;
             }
             try {
                 var payload = JSON.parse(result);
                 callback(payload["args"]["snapshot"]);
             } catch (e) {
                 WebInspector.console.error("Malformed event data in backing storage");
                 callback(null);
             }
         }
     },
 
     /**
+     * @return {!Promise<?>}
+     */
+    objectPromise: function()
+    {
+        if (!this._objectPromise)
+            this._objectPromise = new Promise(this.requestObject.bind(this));
+        return this._objectPromise;
+    },
+
+    /**
      * @override
-     * @param {?function():!Promise.<?string>} backingStorage
+     * @param {?function():!Promise.<?>} backingStorage
      */
     _setBackingStorage: function(backingStorage)
     {
         if (!backingStorage)
             return;
         this._backingStorage = backingStorage;
         this.args = {};
     },
 
     __proto__: WebInspector.TracingModel.Event.prototype
@@ skipping 277 matching lines @@
     /**
      * @return {!Array.<!WebInspector.TracingModel.AsyncEvent>}
      */
     asyncEvents: function()
     {
         return this._asyncEvents;
     },
 
     __proto__: WebInspector.TracingModel.NamedObject.prototype
 }