function VideoProxy(videoElement) {
  this.videoElement = videoElement;
  // True if we're currently manually advancing the playhead (only on iOS).
  this.isFakePlayback = false;

  // When the video started playing.
  this.startTime = null;
}
A proxy class for working around the fact that as soon as a video is play()ed
on iOS, Safari auto-fullscreens the video.

TODO(smus): The entire raison d'etre for this class is to work around this
issue. Once Safari implements some way to suppress this fullscreen player, we
can remove this code.