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Previous to this change, suffixing a "." to the URL from which a
dictionary was being suggested would allow servers to bypass the
check against a subdomain (e.g. evil.protected.good.com) setting a
dictionary to be used by a superdomain (.good.com).

BUG=389451
R=rsleevi@chromium.org

Review URL: https://codereview.chromium.org/574283006

Cr-Commit-Position: refs/heads/master@{#296246}