1218d7ad2f
Changes include the following 1. modify FakeDtlsIdentityStore to support alternate certificate so we could have a different fingerprint in test case. 2. dtlstransportchannel can accept a new fingerprint and trigger DTLS handshake. 3. #2 will trigger new signal on the media side to reset SRTP context. Only reset SRTP context when we are using DTLS (not SDES). 4. Test cases for caller or callee are transfees. TBR=pthatcher@webrtc.org BUG=webrtc:3618 This is a reland of https://codereview.webrtc.org/1453523002 Review URL: https://codereview.webrtc.org/1505573002 . Cr-Commit-Position: refs/heads/master@{#10903}