GitLab

Currently just implements the API layer which allows adding a listener and defines a manifest key to specify mdns service types to watch.

BUG=280900
TBR=erg

Review URL: https://chromiumcodereview.appspot.com/23437015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@221619 0039d316-1c4b-4281-b951-d872f2087c98