Plumbed AudioEncoderFactory up into CreatePeerConnectionFactory.
BUG=webrtc:5806
Review-Url: https://codereview.webrtc.org/2799033006
Cr-Commit-Position: refs/heads/master@{#17977}
Updating GN files, include paths, and include guards
BUG=None
NOTRY=True
NOPRESUBMIT=true
Review-Url: https://codereview.webrtc.org/2387113005
Cr-Commit-Position: refs/heads/master@{#14542}