constructor(originalSource) {
    /**
     * @private @const {!VideoMirrorHelper} manages displaying the video stream
     *     in the page
     */
    this.videoMirrorHelper_ = new VideoMirrorHelper();
    /**
     * @private @const {!MediaStreamSource} original stream source, whose output
     *     is sent on the sender peer connection. In an actual video calling
     *     app, this stream would be generated from the remote participant's
     *     camera. However, in this sample, both sides of the peer connection
     *     are local to allow the sample to be self-contained.
     */
    this.originalStreamSource_ = originalSource;
    /**
     * @private {?PeerConnectionPipe} handles piping the MediaStream through an
     *     RTCPeerConnection
     */
    this.pipe_ = null;
    /** @private {string} */
    this.debugPath_ = '<unknown>';
  }
@param {!MediaStreamSource} originalSource original stream source, whose
    output is sent over the peer connection