GitLab

This CL migrates BackgroundXhrWebstoreTest.PolicyContentScriptXHR to the
CrossOriginReadBlockingExtensionAllowlistingTest test suite (into new
tests, called ContentScriptVsHostBlockedByPolicy_NoSniffXml and
ContentScriptVsHostBlockedByPolicy_AllowedTextResource).

This way the tests covers the following setup aspects:
- CorbAllowlistAlsoAppliesToOorCors feature is enabled or disabled
- Extension is allowlisted or not
- OOR-CORS vs InBlinkCors

After this CL the old test can be deleted.  Note that the old test
always tested with:
- CorbAllowlistAlsoAppliesToOorCors disabled
- Non-allowlisted extension
- The default OOR-CORS state (enabled by default since r728462)

Bug: 1061567
Change-Id: Ic76ac9e48510953fd130141776e66b1fde11c404
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2107431
Commit-Queue: Łukasz Anforowicz <lukasza@chromium.org>
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#754013}