[Android WebView] Disable WebRTC.

Android WebView compiles out WebRTC, so we should disable runtime
interfaces too.

Review URL: https://codereview.chromium.org/25453008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227215 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227215