Previously, `CSSStyleSheet.replace()` and `CSSStyleSheet.replaceSync()`
parsed the given CSS text into a temporary stylesheet object, from
which a list of rules was extracted. Doing this had the unintended
side-effect that a fetch request would be started if the given CSS text
referenced any external resources. This fetch request would cause a
crash, since the temporary stylesheet object didn't set the constructed
flag, or constructor document. We now parse the given CSS text as a
list of rules without constructing a temporary stylesheet.
