AudioTrackMediaSource.idl, TextTrackMediaSource.idl, and VideoTrackMediaSource.idl should be conditional in Sources.txt.
Created attachment 329681 [details] Patch
Comment on attachment 329681 [details] Patch Setting r- due to failed EWS.
I'll look again. This might have changed since I last rebased our branch then.
Yep, this was fixed last month by bug 179372. *** This bug has been marked as a duplicate of bug 179372 ***