b=1069009 add Media Source Extensions to test_interfaces.html r=smaug

--HG--
extra : rebase_source : 2864c15a4fd44b6dc818668704c6f10cf32fd7ad
b=1068964 Remove gtk_check_version for GTK 2 r=karlt

Remove gtk_check_version() checks for GTK 2 as the minimum
version now covers all cases

--HG--
extra : rebase_source : b94f981abe0b0561f6223ae2949559152e46f13e
b=996368 Enable Media Source Extensions for testing r=kinetik

--HG--
extra : rebase_source : 5f7d8897ed8836d80bb22d4cd259fe3a0ce2851f