code: function IFrameMessageSender(iframe) {
    if (!iframe) {
      console.error('No iframe specified');
      return;
    }
    this.iframe = iframe;
  
    // On iOS, if the iframe is across domains, also send DeviceMotion data.
    if (this.isIOS_()) {
      window.addEventListener('devicemotion', this.onDeviceMotion_.bind(this), false);
    }
  }
docs: Sends events to the embedded VR view IFrame via postMessage. Also handles
  messages sent back from the IFrame:
  
  click: When a hotspot was clicked.
  modechange: When the user changes viewing mode (VR|Fullscreen|etc).