Also rename internal::FlexfecReceiveStream to FlexfecReceiveStreamImpl. BUG=webrtc:6849 Review-Url: https://codereview.webrtc.org/2561123002 Cr-Commit-Position: refs/heads/master@{#15666}
BUG=webrtc:5654 Review-Url: https://codereview.webrtc.org/2535173008 Cr-Commit-Position: refs/heads/master@{#15476}
BUG=webrtc:6716 Review-Url: https://codereview.webrtc.org/2550273003 Cr-Commit-Position: refs/heads/master@{#15460}