Implement document.createCSSStyleSheetSync

A new factory function, createCSSStyleSheetSync will allow synchronous
creation of CSSStyleSheet objects that have text but do not have
@import rules. If the sheet text turn out to have @import rules, an
exception will be thrown.

Draft spec at: https://wicg.github.io/construct-stylesheets/
Discussion: https://github.com/WICG/construct-stylesheets/issues/38#issuecomment-423355490

Bug: 807560
Change-Id: I9f8ef4151f616ecc343a12f3ddd0e5a31e1be363
Reviewed-on: https://chromium-review.googlesource.com/c/1237803
Commit-Queue: Rakina Zata Amni <rakina@chromium.org>
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#598731}
15 files changed