Reason for revert: Unfortunately this breaks an internal downstream project since we have an ancient libsrtp. Reverting until we can figure out how to update our libsrtp. Original issue's description: > Remove global list of SRTP sessions. > Instead save a reference to the SrtpSession inside the srtp_ctx_t. > > BUG=webrtc:5133 > > Committed: https://crrev.com/9cafd972779ed7b25886ab276e0ede7b7a8b76a1 > Cr-Commit-Position: refs/heads/master@{#10591} TBR=juberti@google.com,juberti@webrtc.org,jbauch@webrtc.org NOPRESUBMIT=true NOTREECHECKS=true NOTRY=true BUG=webrtc:5133 Review URL: https://codereview.webrtc.org/1442863003 Cr-Commit-Position: refs/heads/master@{#10635}