Removing references to webrtc::PortAllocatorFactoryInterface.

Now using a new CreatePeerConnection method that takes a
PortAllocator as input. This removes the need for some
boilerplate code and code duplication between webrtc and chromium.
It also fixes an issue with TURN candidate priorities.

BUG=webrtc:5209

Review URL: https://codereview.chromium.org/1500663003

Cr-Commit-Position: refs/heads/master@{#364544}
13 files changed