old_contents: 'use strict';
  
  // Define navigator.mediaDevices.getUserMedia() for older devices.
  
  /**
   * Constraints to apply to MediaStream.
   * On this codelab, you will be streaming video, but not audio.
   */
  const mediaStreamConstraints = {
    audio: false,
    video: true,
  };
  
  /** Video element where stream will be placed. */
  const localVideo = document.querySelector('video');
  
  /** Handles success by adding the MediaStream to the video element. */
  const localMediaStreamSuccessCallback = (mediaStream) => {
    window.localStream = mediaStream;  // Makes stream available to the console.
    if (window.URL) {
      localVideo.src = window.URL.createObjectURL(mediaStream);
    } else {
      localVideo.src = mediaStream;
    }
  };
  
  /** Handles error by logging a message to the console with the error message. */
  const localMediaStreamErrorCallback = (error) => {
    console.log('navigator.getUserMedia error: ', error);
  };
  
  // Initializes media stream.
  navigator.mediaDevices.getUserMedia(mediaStreamConstraints)
    .then(localMediaStreamSuccessCallback, localMediaStreamErrorCallback);
  
new_contents: 'use strict';
  
  // Define navigator.mediaDevices.getUserMedia() for older devices.
  
  /**
   * Constraints to apply to MediaStream.
   * On this codelab, you will be streaming video, but not audio.
   */
  const mediaStreamConstraints = {
    audio: false,
    video: true,
  };
  
  /** Video element where stream will be placed. */
  const localVideo = document.querySelector('video');
  
  /** Handles success by adding the MediaStream to the video element. */
  const localMediaStreamSuccessCallback = (mediaStream) => {
    window.localStream = mediaStream;  // Makes stream available to the console.
    if (window.URL) {
      localVideo.src = window.URL.createObjectURL(mediaStream);
    } else {
      localVideo.src = mediaStream;
    }
  };
  
  /** Handles error by logging a message to the console with the error message. */
  const localMediaStreamErrorCallback = (error) => {
    console.log('navigator.getUserMedia error: ', error);
  };
  
  // Initializes media stream.
  navigator.mediaDevices.getUserMedia(mediaStreamConstraints)
    .then(localMediaStreamSuccessCallback)
    .catch(localMediaStreamErrorCallback);
  
subject: Change promise syntax