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By default, OnSSLCertificateError() just cancels current request.
For connectivity_checker, it needs to cancel the current request
and starts next check. In particular, this handles the case that
SSL cert fails when device system time is changing (syncing to
NTP server).

BUG=internal b/20775908

Review URL: https://codereview.chromium.org/1145723004

Cr-Commit-Position: refs/heads/master@{#330557}