[cssom-1] Should CSSStyleSheetInit.baseURL be validated? #12974
Description
baseURL is a CSSStyleSheet.constructor() argument that allows setting the style sheet base URL, which is:
The base URL to use when resolving relative URLs in the stylesheet. Null by default. Only non-null for stylesheets that have constructed flag set.
Chrome always ignores it (WPT). Firefox seems to handle an absolute URL or a relative URL ending with /, eg. /css/, ./css/, css/, but /css, ./css, css, are ignored.
Besides, WPT expects CSSStyleSheet.constructor() to throw NotAllowedError for an invalid base URL, which seems unspecified, noting that the style sheet base URL is used to compute a style resource base URL, while this procedure presumably expects an absolute URL. Should it be absolutized?