Serialize and deserialize dynamic Expect-CT state

This CL serializes/deserializes dynamic Expect-CT state in
TransportSecurityPersister. This is a step in the implementation of the draft
Expect-CT HTTP header
(https://tools.ietf.org/html/draft-ietf-httpbis-expect-ct-00).

BUG=679012

Review-Url: https://codereview.chromium.org/2751803002
Cr-Commit-Position: refs/heads/master@{#465436}
3 files changed