Combine CTVerifier usage into CertAndCTVerifier

Adds a CertAndCTVerifier class, which is a new CertVerifier wrapper type
which composes certificate and certificate transparency (CT)
verification as part of CertVerifier::Verify(). This also removes all
direct usage of CTVerifier, making the only "public" API the
CertVerifier::Verify() API.

This also fixes MockCertVerifier to fix a violation of the API contract
of CertVerifier::Verify(). Now it is guaranteed that deleting the
verifier will result in any outstanding Requests to be canceled and
their callbacks reset.

As a side effect, this allows MockCertVerifier to control both cert and
CT results in CertVerifyResult in tests (particularly useful in
integration tests where setting up test certs with valid SCT is
challenging).

Bug: 848277
Change-Id: If37fe21f0f5328a0a48a964d9525066614ce0439
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2531113
Reviewed-by: Joe Downing <joedow@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Ryan Sleevi <rsleevi@chromium.org>
Commit-Queue: Chris Thompson <cthomp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830855}