Bug 977299 - Don't display subtitles if their mode is 'hidden'. r=rillian

I've renamed TextTrackList::GetAllActiveCues to
UpdateAndGetShowingCues to make it a bit more clear what
this function is doing.
Bug 983577 - Improvements to parallel and sequential map for TypedObject. r=shu
Bug 984004 - Part 1: Cache parent's fullZoom\textZoom value to ensure that we always return the fresh one. r=felipc
Bug 984004 - Part 2: Immediately update %label on reset. r=felipc
Bug 985770 - MemoryTextureClient should use array delete in destructor. r=Bas