Fix CSSPreloadScanner to avoid missing rules (reland)

This fixes a couple of bugs with the CSSPReloadScanner that made it miss
rules in which the URL wasn't quoted or the rule didn't end with a
semicolon. It also adds tentative WPT tests for that functionality, as
the tests are also relevant for WebKit.

This is a reland of
https://chromium-review.googlesource.com/c/chromium/src/+/1331042

Bug: 903785
Change-Id: I401c252a42fbb96dee9c7942e0a4f8d5b6850244
TBR: kouhei
Reviewed-on: https://chromium-review.googlesource.com/c/1349980
Reviewed-by: Yoav Weiss <yoav@yoav.ws>
Commit-Queue: Yoav Weiss <yoav@yoav.ws>
Cr-Commit-Position: refs/heads/master@{#610796}
7 files changed