API test for WebRTC logging extension.

The part testing the multipart data has taken from chrome/browser/media/chrome_webrtc_browsertest.cc (RunsAudioVideoWebRTCCallInTwoTabsWithLogging).

BUG=298158

Review URL: https://codereview.chromium.org/38783006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231015 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 231015