Bug 1511256 - disabled test_videocontrols.html on linux r=jmaher

--HG--
extra : rebase_source : 2e78219ed1d980881dd317cb8fa831d8d8be67a8

toolkit/content/tests/widgets/xbl/mochitest.ini

@@ -26,7 +26,7 @@ support-files =
 [test_audiocontrols_dimensions.html]
 [test_videocontrols.html]
 tags = fullscreen
-skip-if = toolkit == 'android' || (verify && debug && (os == 'linux')) #TIMED_OUT
+skip-if = toolkit == 'android' || (verify && debug && (os == 'linux')) || (os == 'linux') #TIMED_OUT, Bug 1511256
 [test_videocontrols_keyhandler.html]
 skip-if = (toolkit == 'android') || (os == 'linux') #Bug 1366957
 [test_videocontrols_vtt.html]