[css-ui-4] Fallout of change from resulting from https://github.com/w3c/csswg-drafts/issues/11494

[weinig]

In #11494 (comment), it was decided that:

Summary of the resolution as I understand it:

1. column-rule-*, border-*, and outline-* are all under consideration
2. Computed value for *-width should be independent of *-style, i.e. remove the none/hidden special behavior from this stage
3. Resolved value (i.e. getComputedStyle) for border-width should continue to return 0 if border-style is none/hidden, for compat reasons
4. If also needed for compat, apply 3 to outline-width and column-rule-width as well

I implemented this in WebKit very recently, and we have so far received one regression report: https://bugs.webkit.org/show_bug.cgi?id=306818.

In the report, the authors code was assuming that the computed style of outline-width would be 0 when outline-style was none.

I'm not clear on exactly what criteria we should apply for considering instituting step 4 for outline-width (e.g. giving outline-width a resolved value of 0 when outline-style is none), this is one data point in favor of it.

cc kbabbitt @emilio @fantasai @tabatkins

[KuznetsovRoman]

Providing code example, where i encountered regression (css - is a result of gCS):
https://github.com/gemini-testing/testplane/blob/master/src/browser/client-scripts/index.js#L322-L331

Its piece of client script, which is supposed to calculate coords of an element so we could extract that area from viewport screenshot:
https://github.com/gemini-testing/testplane/blob/master/src/browser/client-scripts/index.js#L303

It is supposed to return coords with outlines (if there are any), but when executing in new browsers, it always returns coords like there is 3px outline, even there is none.

The fix on our side is simple (gemini-testing/testplane#1198), but since Testplane is a tool, our users would need to update it