See also upstream's 06cf881a3a10d5af3c1255c08cfd0c6ddb5f1cc3,
9f040d6decca7930e978784c917f731e5c45e8f0, and
9f6795e7d2.
Change-Id: I27d90e382867a5fe988d152b31f8494e001a6a9f
Reviewed-on: https://boringssl-review.googlesource.com/6628
Reviewed-by: Adam Langley <agl@google.com>