Support full color glyphs

[jrmuizel]

This is needed for Emoji

[LifeIsStrange]

Maybe I am saying bullshit because I'm not a programmer but couldn't webrender just use Cairo for this since it support it ?
http://www.phoronix.com/scan.php?page=news_item&px=Cairo-1.15.8-Colored-Emoji

[jrmuizel]

At least on Mac these already work. On Linux it's probably not worth taking a cairo dependency just so we can decode the png's in the fonts.

[glennw]

I think it's relatively simple for Linux - we just need to tell FreeType we want color glyphs to be supported, and then handle the image glyph type. I'm not sure what's involved for Windows yet.

[glennw]

@lsalzman This is complete on all platforms, I think?

[glennw]

@lsalzman Anything else to do here?

[lsalzman]

This is done.