Picture in Picture test not waiting for event handlers

[theIDinside]

The test https://github.com/web-platform-tests/wpt/blob/2fe220b448/picture-in-picture/leave-picture-in-picture.html is not waiting for event handlers to run, therefore will pass without asserts running.

Also, the second test in this file is an optional test, see the disable attribute. Therefore it should be split up into a new file with .optional component in the file name.

[marcoscaceres]

@theIDinside great to be filing bugs for pip! Make sure you label them though so they are easy for us to find... there's so many bugs in this repo that sometimes things get lost.

Might also be good to file a bug on the spec reminding us to update the test suite 🙈