Change the default rtcp mux policy from negotiate to require.
After monitoring the UMA stats, the plan is to change the default rtcp mux policy from negotiated to require.
According to the UMA data in 28 days, 99.96% users choose the default value of rtcp mux policy which means nearly all the users who are using "negotiate" policy would be affected by this change. Because among all the users with media, only 3% disabled the rtcp mux so it's not risky to make this change.
The UMA "SelectedRtcpMuxPolicy" is removed in this CL since it is only used to gauge the risk of this change.
BUG=webrtc:6030
Review-Url: https://codereview.chromium.org/2055553003
Cr-Commit-Position: refs/heads/master@{#439955}
10 files changed
