waitForMovementOrFailOnTimeout(target, timeout) {
    this.timeoutAfter(timeout).failOnTimeout(true);
    return this.waitForMovement(target);
  }
Wait for the video playhead to move forward by some meaningful delta.
If this happens before |timeout| seconds pass, the Promise is resolved.
Otherwise, the Promise is rejected.

@param {!HTMLMediaElement} target
@param {number} timeout in seconds, after which the Promise fails
@return {!Promise}