The canonicalization of the path component of mailto urls is too lax,
leading to information disclosure and possible command injection attacks
against mail clients. To fix this, we percent-encode more characters in
the path component of mailto urls, matching other Firefox/IE/Edge.

The original land of this patch (via 2817213002) omitted an update to
layout tests.

BUG=711020
TEST=url_unittests,run-webkit-tests fast/url

Review-Url: https://codereview.chromium.org/2820373002
Cr-Commit-Position: refs/heads/master@{#465357}