WebRTC should generate default private address even when adapter enumeration is disabled.

Introduce a DefaultAddressProvider such that rtc::Network can't access other part of NetworkManager.

This also removes the hack of generating the loopback address. The dependency has been removed by https://codereview.chromium.org/1417023003/

BUG=webrtc:5061
R=pthatcher@webrtc.org

Review URL: https://codereview.webrtc.org/1411253008 .

Cr-Original-Commit-Position: refs/heads/master@{#10590}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 9af97f89103d8f1f77b52a6ae77b8b7bcdc23f71
12 files changed