Add an OWNERS file for the WebRTC IPC messages file

BUG=none
TBR=cdn@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/138023006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244856 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244856