static anyMediaElement() {
    if (shaka.util.Dom.cachedMediaElement_) {
      return shaka.util.Dom.cachedMediaElement_;
    }

    if (!shaka.util.Dom.cacheExpirationTimer_) {
      shaka.util.Dom.cacheExpirationTimer_ = new shaka.util.Timer(() => {
        shaka.util.Dom.cachedMediaElement_ = null;
      });
    }

    shaka.util.Dom.cachedMediaElement_ = /** @type {HTMLMediaElement} */(
      document.getElementsByTagName('video')[0] ||
      document.getElementsByTagName('audio')[0]);

    if (!shaka.util.Dom.cachedMediaElement_) {
      shaka.util.Dom.cachedMediaElement_ = /** @type {!HTMLMediaElement} */(
        document.createElement('video'));
    }

    shaka.util.Dom.cacheExpirationTimer_.tickAfter(/* seconds= */ 1);
    return shaka.util.Dom.cachedMediaElement_;
  }
For canPlayType queries, we just need any instance.

First, use a cached element from a previous query.
Second, search the page for one.
Third, create a temporary one.

Cached elements expire in one second so that they can be GC'd or removed.

@return {!HTMLMediaElement}