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The canonicalization of file URLs effectively lowercases IPv6
addresses. This confuses GetCookieDomainWithString; when it determines
the host is an IP address, it checks whether the specified domain is
an exact match to the URL's host. This exact string match works fine
for IPv4 addresses, because lowercasing them has no effect.

Suppose the URL is "file://[A::]" and the domain is "[A::]". Because
the URL's host was canonicalized as "[a::]", the exact match will
fail.

The reason the linked Clusterfuzz bug only reproduced on Windows is
that it relies on Windows-specific behavior that turns URLs that
resemble UNC paths (prefixed with two backslashes) into file URLs.

Bug: 986675
Change-Id: I66b81dcd499a36132bdf39e42479425e427f0c4c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1726989Reviewed-by: Maks Orlovich <morlovich@chromium.org>
Commit-Queue: Dan McArdle <dmcardle@chromium.org>
Cr-Commit-Position: refs/heads/master@{#685320}