DevTools: adopt FilmStripModel to new screenshot recorder trace format

Source/devtools/front_end/sdk/TracingModel.js

Index: Source/devtools/front_end/sdk/TracingModel.js
diff --git a/Source/devtools/front_end/sdk/TracingModel.js b/Source/devtools/front_end/sdk/TracingModel.js
index 5259db5484e2208aad02df0d350f1e0f19a720f4..9d1b7ae017ad91164507be5ec9491c7b52e4ea19 100644
--- a/Source/devtools/front_end/sdk/TracingModel.js
+++ b/Source/devtools/front_end/sdk/TracingModel.js
@@ -718,6 +718,14 @@ WebInspector.TracingModel.ObjectSnapshot.prototype = {
     },
 
     /**
+     * @return {!Promise<?Object>}
+     */
+    objectPromise: function()
+    {
+        return new Promise(this.requestObject.bind(this));
+    },
+
+    /**
      * @override
      * @param {?function():!Promise.<?string>} backingStorage
      */