Add content_browser test for remote video track relaying.

BUG=webrtc 383
R=perkj@chromium.org, phoglund@chromium.org, phoglund@google.com, xians@chromium.org

Review URL: https://codereview.chromium.org/23542038

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225202 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225202