Shim for MediaDevices#getUserMedia method
@param {object} constraints - The user media constraints
function getUserMedia (constraints) {
  if (props('navigator.mediaDevices.getUserMedia').hadBy(window)) {
    let medias = props('navigator.mediaDevices').from(window)
    return medias.getUserMedia(constraints)
  }
  let userMediaGetter = navigator.getUserMedia ||
                        navigator.webkitGetUserMedia ||
                        navigator.mozGetUserMedia ||
                        navigator.msGetUserMedia
  if (!userMediaGetter) {
    throw new Error('getUserMedia is not supported by this browser')
  }
  return new Promise((resolve, reject) => {
    userMediaGetter(constraints, resolve, reject)
  })
}