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m.foo.com can set cookies on foo.com, so when checking for cookies in
the eligibility code path, any cookie applicable to the same or higher
domain up until TLD should cause the prefetch to be non-eligible.

Also adds some browsertesting in the same vein.

Bug: 1096765
Change-Id: I23801d45bbdd789b52977613bf1086deda166460
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2264933Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Commit-Queue: Robert Ogden <robertogden@chromium.org>
Cr-Commit-Position: refs/heads/master@{#782033}