[DevTools] Turn starting tracing into promise.

third_party/WebKit/Source/devtools/front_end/sdk/ResourceTreeModel.js

 /*
  * Copyright (C) 2011 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 338 matching lines @@
       this.reloadPage.apply(this, this._pendingReloadOptions);
   }
 
   /**
    * @param {boolean=} bypassCache
    * @param {string=} scriptToEvaluateOnLoad
    */
   reloadPage(bypassCache, scriptToEvaluateOnLoad) {
     // Only dispatch PageReloadRequested upon first reload request to simplify client logic.
     if (!this._pendingReloadOptions)
-      this.dispatchEventToListeners(SDK.ResourceTreeModel.Events.PageReloadRequested);
+      this.dispatchEventToListeners(SDK.ResourceTreeModel.Events.PageReloadRequested, this);
     if (this._reloadSuspensionCount) {
       this._pendingReloadOptions = [bypassCache, scriptToEvaluateOnLoad];
       return;
     }
     this._pendingReloadOptions = null;
     this.dispatchEventToListeners(SDK.ResourceTreeModel.Events.WillReloadPage);
     this._agent.reload(bypassCache, scriptToEvaluateOnLoad);
   }
 
   /**
@@ skipping 514 matching lines @@
     this._resourceTreeModel.dispatchEventToListeners(SDK.ResourceTreeModel.Events.InterstitialHidden);
   }
 
   /**
    * @override
    */
   navigationRequested() {
     // Frontend is not interested in when navigations are requested.
   }
 };