Move the FEC enabling logic from CodecManager to Rent-A-Codec

BUG=webrtc:5028

Review URL: https://codereview.webrtc.org/1476743002

Cr-Original-Commit-Position: refs/heads/master@{#10785}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 9cd5c8ca79dbfaecb6101e0635b9cb8699875784
3 files changed