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This relands crrev.com/c/691663 which confirms that nostate prefetch
sets cookies on all fetches. In the interim a test for cross-domain
fetches has been added.

The original CL was reverted due to flakes on windows. I could not
reliably reproduce the flakes, but in addition to the usual CQ, I've
run this several times on the windows bots, and it is no longer
flaking. Perhaps commit e23356c2 which moved browser_test_utils to
mojo access of cookies removed whatever race existed, or perhaps using
PostDelayedTask instead of sleeping fixed it.

Bug: 
Change-Id: I71ef3053c71da53e21093dc57d977e3992d279ef
Reviewed-on: https://chromium-review.googlesource.com/695221
Commit-Queue: Matthew Cary <mattcary@chromium.org>
Reviewed-by: Egor Pasko <pasko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522067}