This CL avoids changing the mentioned callbacks during a call, to avoid a potential deadlock when acquiring _sendCritSect and calling _mediaOpt.SetTargetRates. Moving the critsect revealed a race for the FEC parameters in RtpVideoSender, so the CL grew a bit to avoid this. I also cleaned up some code here at the same time, but tried to keep it at a minimum since this CL had already increased a lot in size. BUG=769 R=pbos@webrtc.org, stefan@webrtc.org Review URL: https://webrtc-codereview.appspot.com/42939004 Cr-Commit-Position: refs/heads/master@{#8899}