_initAdsManagerEventListeners () {
    const adsManager = this.adsManager

    // https://developers.google.com/interactive-media-ads/docs/sdks/html5/client-side/reference/js/google.ima.AdErrorEvent
    adsManager.addEventListener(
      google.ima.AdErrorEvent.Type.AD_ERROR,
      this._onAdsManagerAdError
    )

    // https://developers.google.com/interactive-media-ads/docs/sdks/html5/client-side/reference/js/google.ima.AdEvent
    const adEvents = [
      'LOADED',
      'STARTED',
      'RESUMED',
      'PAUSED',
      'COMPLETE',
      'ALL_ADS_COMPLETED',
      'CONTENT_PAUSE_REQUESTED',
      'CONTENT_RESUME_REQUESTED',
      'VOLUME_CHANGED',
      'VOLUME_MUTED',
      'AD_METADATA',
      'AD_CAN_PLAY',
      'AD_PROGRESS',
      'AD_BUFFERING',
      'CLICK',
      'VIDEO_CLICKED',
      'VIDEO_ICON_CLICKED',
      'FIRST_QUARTILE',
      'MIDPOINT',
      'THIRD_QUARTILE',
      'SKIPPED',
      'USER_CLOSE',
      'AD_BREAK_READY',
      'AD_BREAK_FETCH_ERROR'
    ]
    adEvents.forEach(type => {
      adsManager.addEventListener(google.ima.AdEvent.Type[type], this.onAdEvent)
    })
  }
Handles the ad manager loading and sets ad event listeners.
@private