Roll webrtc to r4883.

R=ronghuawu@chromium.org

Review URL: https://codereview.chromium.org/25106005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226054 0039d316-1c4b-4281-b951-d872f2087c98
Update .DEPS.git

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226055 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226054
SVN changes up to revision 226055