[cssom-1] Merge constructable stylesheets into CSSOM (https://lists.w3.org/Archives/Public/www-style/2020Feb/0012.html)

[mfreed7]

[cssom-1] Merge constructable stylesheets into CSSOM (https://lists.w3.org/Archives/Public/www-style/2020Feb/0012.html)

This is a first PR to merge the Constructable Stylesheets proposal into the CSSOM spec. This was resolved in Feb 2020: https://lists.w3.org/Archives/Public/www-style/2020Feb/0012.html. There are several sub-resolutions there, a few of which are handled here:

• RESOLVED: CSS() is merged into CSSOM1 (either @emilio or @rakina @mfreed7 doing so).
• RESOLVED: Remove title and alternate from constructor.
• RESOLVED: Add base URL constructor argument for sole purpose of resolving relative URLs in stylesheet, and location of the stylesheet remains that of the document.
• RESOLVED: Disallow @import in all constructable stylesheet apis with a note that we're doing it to match current state of modules and this might relax in future. Plus the modifications discussed in this comment.

...and a few of which will follow this PR:

• RESOLVED: Constructed style sheets to always go after. (Which spec does this live inside?)
• Modify URL parsing to take the new CSSStyleSheet base URL into account. (Suggestions appreciated for where exactly these specs live. These two perhaps? referrer-policy css-values-4)
• Make adopted stylesheets a CSSStyleSheetList and add the appropriate add/remove methods to the document or shadowRoot interface an ObservableArray.

Closes #3433, Closes WICG/construct-stylesheets#102, Closes WICG/construct-stylesheets#90

P.S. This is my first CSSWG PR. Please go easy on me and let me know what I can do better. 😄

[mfreed7]

Any thoughts here? @emilio

[emilio]

Hey, sorry for the lag. This looks sensible to me. Maybe @tabatkins has some editorial comments or something? But otherwise this seems good to merge to me.

I assume the DocumentOrShadowRoot.adoptedStyleSheets etc definitions should get merged-in later?

[mfreed7]

Hey, sorry for the lag. This looks sensible to me. Maybe @tabatkins has some editorial comments or something? But otherwise this seems good to merge to me.

I assume the DocumentOrShadowRoot.adoptedStyleSheets etc definitions should get merged-in later?

Great, thanks! I'm happy to make modifications, just let me know.

As for adoptedStyleSheets, yes, I was thinking about handling that in a followup PR, just to separate constructable stylesheets from their use. If you think it needs to be combined, let me know.

[mfreed7]

Hey, sorry for the lag. This looks sensible to me. Maybe @tabatkins has some editorial comments or something? But otherwise this seems good to merge to me.
I assume the DocumentOrShadowRoot.adoptedStyleSheets etc definitions should get merged-in later?

Great, thanks! I'm happy to make modifications, just let me know.

As for adoptedStyleSheets, yes, I was thinking about handling that in a followup PR, just to separate constructable stylesheets from their use. If you think it needs to be combined, let me know.

Any further thoughts @emilio @tabatkins ? Anything else I need to do in order to get this landed?

[mfreed7]

Any further thoughts @emilio @tabatkins ? Anything else I need to do in order to get this landed?

Friendly ping @emilio and @tabatkins, thanks!

[emilio]

LGTM, thanks for this @mfreed7 (and sorry, I'm really slow with gh notifications lately :/)

[mfreed7]

LGTM, thanks for this @mfreed7 (and sorry, I'm really slow with gh notifications lately :/)

No problem at all (I'm even more guilty of that) and thanks for merging this.

I will now get started on the other parts, mentioned in the original comment here.