Support rgb and hsl new syntax in CSS Color Level 4

[upsuper]

That is, to

• make rgb an alias of rgba
• make hsl an alias of hsla
• make alpha channel optional for all functions above
• accept whitespace splited form

https://drafts.csswg.org/css-color-4/#rgb-functions
https://drafts.csswg.org/css-color-4/#the-hsl-notation

[SimonSapin]

Do you know what the implementation status of this is in other engines?

[upsuper]

Gecko supports the new syntax for these four functions (and I saw test failures in Gecko's test with stylo because of lack of the support of them).

Gecko's implementing bug for this seems to be bug 1295456 but I don't see an intent to ship for this.

It seems to me that no any other engine is shipping this. That reminds me that we probably should inform the working group that Gecko is shipping it.

[upsuper]

In addition to what I've mentioned above, the functions also accept <number>s and <percentage>s for all components rather than only <integer>.

[manuel-woelker]

I'd like to tackle this one. Let me know if anyone else is currently working on this.

It look to be relatively straightforward. I'd probably need to update some test cases in color3.json that are now valid.

I'd like to use the test spec cases to add additional test cases:
http://test.csswg.org/suites/css-color-4_dev/nightly-unstable/html/chapter-4.htm

[SimonSapin]

Yes, please add new test cases (and modify existing ones as needed) in color3.json, and extend make_color3_hsl.py as well. It is used like so: python2 make_color3_hsl.py > color3_hsl.json.

Feel free to ask here or on #servo IRC if you have any question.