addListener() {
    if (this.hasListener_) {
      return;
    }
    this.hasListener_ = true;
    this.doAddListener_();
  }
/**
   * Adds event listener. No-ops if listener is already added. Event
   * listeners will be added back automatically the next time extension wakes
   * up, during |addOnStartup|.
   */
Adds event listener. No-ops if listener is already added. Event
listeners will be added back automatically the next time extension wakes
up, during |addOnStartup|.
Adds event listener . No - ops if listener is already added . Event listeners will be added back automatically the next time extension wakes up during |addOnStartup| .
addListener() {
    if (this.hasListener_) {
      return;
    }
    this.hasListener_ = true;
    this.doAddListener_();
  }
addListener ( ) { if ( this . hasListener_ ) { return ; } this . hasListener_ = true ; this . doAddListener_ ( ) ; }
Adds event listener.
Adds event listener .