Another requirement to have transparency in videos. Straight port of Firefox 53 implementation, save for some oddities relating to needing to put uint8_t instead of uint8 in yuv_convert to get this to compile.
Ref: BZ 1321076, 1329104
Required to have an alpha channel (which in the strange world of graphics seems to refer to transparency, and not experimental code) in WebM videos. Straight port of Firefox 53 implementation, adapted slightly for a couple of patches previously taken without this.
Ref: BZ 1320829
Since these are just interpreted comments, there's 0 impact on actual code.
This removes all lines that match /* vim: set(.*)tw=80: */ with S&R -- there are
a few others scattered around which will be removed manually in a second part.
