Style fixes in FecReceiver and ProducerFec unit tests.

- Change some types to size_t.
- Update parameter ordering.
- Run 'git cl format'
- Moved 'using declarations' into unnamed namespaces.
- Removed "::webrtc::" prefix from some using declarations.

BUG=webrtc:5654

Review-Url: https://codereview.webrtc.org/2273353002
Cr-Original-Commit-Position: refs/heads/master@{#14475}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 71ca74798af8fd33a55ddd462945289b920103f2
4 files changed