Add virtual Initialize methods to PortAllocator and NetworkManager.

This will allow PeerConnection to handle hopping to the right thread
and doing thread-specific initialization for the PortAllocator.
This eliminates a required thread-hop for whatever is passing the
PortAllocator into CreatePeerConnection.

BUG=617648
R=pthatcher@webrtc.org, skvlad@webrtc.org

Review URL: https://codereview.webrtc.org/2097653002 .

Committed: https://crrev.com/a6bdb0990a659ff9e7c4374f5033a6bcc4fbfb21
Cr-Original-Commit-Position: refs/heads/master@{#13306}
Cr-Original-Original-Commit-Position: refs/heads/master@{#13283}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: f8e65779a7dc890d8d6f38eca50985a2f0407da1
5 files changed