addEventListener(eventName, listener) {
    if (!this.eventListeners_.has(eventName)) {
      this.eventListeners_.set(eventName, new Map());
    }
    let id = this.nextListenerId_++;
    this.eventListeners_.get(eventName).set(id, listener);
    this.eventListenerIdToEventName_.set(id, eventName);
    return id;
  }
/**
   * Listens for DevTools protocol events of the specified name and issues the
   * callback upon reception.
   *
   * @param {string} eventName Name of the DevTools protocol event to listen
   *     for.
   * @param {!chromium.DevTools.Connection.EventFunction} listener The callback
   *     issued when we receive a DevTools protocol event corresponding to the
   *     given name.
   * @return {number} The id of this event listener.
   */
Listens for DevTools protocol events of the specified name and issues the
callback upon reception.

@param {string} eventName Name of the DevTools protocol event to listen
for.
@param {!chromium.DevTools.Connection.EventFunction} listener The callback
issued when we receive a DevTools protocol event corresponding to the
given name.
@return {number} The id of this event listener.
Listens for DevTools protocol events of the specified name and issues the callback upon reception . @param { string } eventName Name of the DevTools protocol event to listen for . @param { !chromium . DevTools . Connection . EventFunction } listener The callback issued when we receive a DevTools protocol event corresponding to the given name . @return { number } The id of this event listener .
addEventListener(eventName, listener) {
    if (!this.eventListeners_.has(eventName)) {
      this.eventListeners_.set(eventName, new Map());
    }
    let id = this.nextListenerId_++;
    this.eventListeners_.get(eventName).set(id, listener);
    this.eventListenerIdToEventName_.set(id, eventName);
    return id;
  }
addEventListener ( eventName , listener ) { if ( ! this . eventListeners_ . has ( eventName ) ) { this . eventListeners_ . set ( eventName , new Map ( ) ) ; } let id = this . nextListenerId_ ++ ; this . eventListeners_ . get ( eventName ) . set ( id , listener ) ; this . eventListenerIdToEventName_ . set ( id , eventName ) ; return id ; }
Listens for DevTools protocol events of the specified name and issues the
 callback upon reception.
Listens for DevTools protocol events of the specified name and issues the callback upon reception .