Add once field to devtools so it can be queried by lighthouse.

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

 /*
  * Copyright (C) 2012 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 589 matching lines @@
 /**
  * @unrestricted
  */
 WebInspector.EventListener = class extends WebInspector.SDKObject {
   /**
    * @param {!WebInspector.Target} target
    * @param {!WebInspector.RemoteObject} eventTarget
    * @param {string} type
    * @param {boolean} useCapture
    * @param {boolean} passive
+   * @param {boolean} once
    * @param {?WebInspector.RemoteObject} handler
    * @param {?WebInspector.RemoteObject} originalHandler
    * @param {!WebInspector.DebuggerModel.Location} location
    * @param {?WebInspector.RemoteObject} removeFunction
    * @param {string=} listenerType
    */
   constructor(
       target,
       eventTarget,
       type,
       useCapture,
       passive,
+      once,
       handler,
       originalHandler,
       location,
       removeFunction,
       listenerType) {
     super(target);
     this._eventTarget = eventTarget;
     this._type = type;
     this._useCapture = useCapture;
     this._passive = passive;
+    this._once = once;
     this._handler = handler;
     this._originalHandler = originalHandler || handler;
     this._location = location;
     var script = location.script();
     this._sourceURL = script ? script.contentURL() : '';
     this._removeFunction = removeFunction;
     this._listenerType = listenerType || 'normal';
   }
 
   /**
@@ skipping 11 matching lines @@
   }
 
   /**
    * @return {boolean}
    */
   passive() {
     return this._passive;
   }
 
   /**
+   * @return {boolean}
+   */
+  once() {
+    return this._once;
+  }
+
+  /**
    * @return {?WebInspector.RemoteObject}
    */
   handler() {
     return this._handler;
   }
 
   /**
    * @return {!WebInspector.DebuggerModel.Location}
    */
   location() {
@@ skipping 110 matching lines @@
         this._type === 'wheel';
   }
 
   /**
    * @return {boolean}
    */
   isNormalListenerType() {
     return this._listenerType === 'normal';
   }
 };