service worker: Add test for CSS cross-origin access.

Tests for https://chromium-review.googlesource.com/c/chromium/src/+/1088335

Bug: 848786
Change-Id: I39d71d9aa2d1c0522c7a386405128297f62a0b24
Reviewed-on: https://chromium-review.googlesource.com/1088719
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Reviewed-by: Tsuyoshi Horo <horo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565208}
7 files changed