merge_pr_47863

Make @import prelude parsed using the streaming parser.

There is one exception still: If there's a media query in there,
it is still parsed using the non-streaming parser. However, the
supports part and the prelude in general are parsed streaming.

Note that this fixes a bug (also in the tests) where empty supports(),
or supports() with an invalid declaration inside, would be allowed;
there doesn't seem to be any allowance for this in the grammar
( is not included in the @import grammar, only in
@supports).

Bug: 1500904
Change-Id: Ida837291feac344e847b0e3982acff9dd73c7d53
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5822594
Commit-Queue: Steinar H Gunderson [email protected]
Reviewed-by: Anders Hartvoll Ruud [email protected]
Cr-Commit-Position: refs/heads/main@{#1348630}