Add new mirror for AppRTC due to code move at GitHub.

This mirror will be replaced by a Chrome infra mirror
as soon as is fixed.

TESTED=Successfully ran gclient runhooks in a checkout with
the webrtc.DEPS solution added and the old webrtc-samples dir

Review URL:

git-svn-id: 4ff67af0-8c30-449e-8e8b-ad334ec8d88c
5 files changed