Replacing SSLIdentity* with scoped_refptr<RTCCertificate> in TransportChannel layer.

BUG=webrtc:4927
R=tommi@webrtc.org, torbjorng@webrtc.org

Review URL: https://codereview.webrtc.org/1304043008 .

Cr-Commit-Position: refs/heads/master@{#9885}
14 files changed