API test WebKit2.MSEIsPlayingAudio timing out after r200951

API test WebKit2.MSEIsPlayingAudio timing out after r200951
https://bugs.webkit.org/show_bug.cgi?id=157748

Reviewed by Eric Carlson.

The file-with-mse.html testcase only calls play() once it's own XHR loading is complete; the
"user gesture" check fails at that point.  Call play() up front; playback will begin as soon
as enough data is loaded.

* TestWebKitAPI/Tests/WebKit2/file-with-mse.html:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@200978 268f45cc-cd09-0410-ab3c-d52691b4dbfc