Fix a test failure when IP Permission check is turned on

Fix a test failure when IP Permission check is turned on.

With IP Permission check, there might not be connectivity as the STUN server is specified but there is no internet connectivity. Add loopback interface to ensure there is always connectivity.

BUG=520101
Committed: https://crrev.com/f08e419e94f6d52db5c3bec4b0d5cd29f9901ef4
Cr-Commit-Position: refs/heads/master@{#352657}

[guoweis_left_chromium, 2015-10-06 17:43:56]

guoweis@chromium.org changed reviewers:
+ dalecurtis@chromium.org

[guoweis_left_chromium, 2015-10-06 17:43:57]

PTAL.

[guoweis_left_chromium, 2015-10-06 17:46:14]

guoweis@chromium.org changed reviewers:
- dalecurtis@chromium.org

[guoweis_left_chromium, 2015-10-06 17:46:34]

guoweis@chromium.org changed reviewers:
+ xhwang@chromium.org

[guoweis_left_chromium, 2015-10-06 17:46:34]

PTAL.

[xhwang, 2015-10-06 17:50:40]

not super familiar with this code, but it seems to make sense to me.

rs LGTM

[guoweis_left_chromium, 2015-10-06 17:51:48]

The CQ bit was checked by guoweis@chromium.org

[commit-bot: I haz the power, 2015-10-06 17:52:05]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1381703006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1381703006/1

[commit-bot: I haz the power, 2015-10-06 19:07:31]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-06 19:08:22]

Patchset 1 (id:??) landed as
https://crrev.com/f08e419e94f6d52db5c3bec4b0d5cd29f9901ef4
Cr-Commit-Position: refs/heads/master@{#352657}