exitVR(display) {
    return display.exitPresent()
      .then(
        ()=> {
          this.presentedSource = undefined;
        },
        // this could fail if:
        // 1. exit requested while not currently presenting
        ()=> this.__setState(State.ERROR_EXIT_PRESENT_REJECTED)
      );
  }
Exit presentation mode on display
@param {VRDisplay} display
@return {Promise.<TResult>}