RTPSender::sending_media_ should be guarded by send_critsect_. Fix this in GetSendSideDelay, SendPadData and TimeToSendPadding. Also add appropriate thread annotations. BUG=3029 R=stefan@webrtc.org Review URL: https://webrtc-codereview.appspot.com/9779004 git-svn-id: http://webrtc.googlecode.com/svn/trunk@5697 4adac7df-926f-26a2-2b94-8c16560cd09d