[css-color-6] add color functions for some (or all) compositing/blending operations

[chromium-helper]

CSSWG added the following resolution(s):

• RESOLVED: color-layers([<blend-mode>, ]? <color>#)
• RESOLVED: function name is "color-layers()"

in w3c/csswg-drafts#8431 (comment)

[chromium-helper]

I have filed issues.chromium.org/358210825

That is all that can be done here, closing issue.