Case: invlke play() and the pause() on an element that already has enough data to play.
Expected result: resolve the promise.
MozReview-Commit-ID: BdbYHf7moyH
--HG--
extra : rebase_source : c0fa86c888c936f9a19622c74e135e5aafdbc754
extra : source : de021cfd2633cb7c0bc307ce67fe80b54010bd93
Kaku Kuo