Replacing SSLIdentity* with scoped_refptr<RTCCertificate> in the cricket::TransportDescriptionFactory layers.

Updates TransportDescriptionFactory, calls and unittests.

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

Review URL: https://codereview.webrtc.org/1311903004 .

Cr-Commit-Position: refs/heads/master@{#9815}
6 files changed