[DevTools] Turn starting tracing into promise.

third_party/WebKit/Source/devtools/front_end/Tests.js

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 894 matching lines @@
       }
       override.apply(original, arguments);
       return value;
     };
   };
 
   TestSuite.prototype.startTimeline = function(callback) {
     var test = this;
     this.showPanel('timeline').then(function() {
       var timeline = UI.panels.timeline;
-      test._overrideMethod(timeline, 'recordingStarted', callback);
+      test._overrideMethod(timeline, '_recordingStarted', callback);
       timeline._toggleRecording();
     });
   };
 
   TestSuite.prototype.stopTimeline = function(callback) {
     var timeline = UI.panels.timeline;
     this._overrideMethod(timeline, 'loadingComplete', callback);
     timeline._toggleRecording();
   };
 
@@ skipping 176 matching lines @@
       if (runtimeModel.executionContexts().length >= n)
         callback.call(null);
       else
         this.addSniffer(SDK.RuntimeModel.prototype, '_executionContextCreated', checkForExecutionContexts.bind(this));
     }
   };
 
 
   window.uiTests = new TestSuite(window.domAutomationController);
 })(window);