Add SocketFactoryInterface::Prepare and fix how symmetric NAT is determined.

Also remove Bind from ServerSocket interface as it's not needed anymore.

BUG=4576
R=pthatcher@webrtc.org

Review URL: https://codereview.webrtc.org/1162263012

Cr-Original-Commit-Position: refs/heads/master@{#9371}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: d04d3d73ebac96c265da1527328e7c96ecc5e996
3 files changed