Mac OS X-specific implementation of Networking Private API. 
Based on infrastructure in http://crrev.com/54323003

BUG=330255

Review URL: https://codereview.chromium.org/64683014

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247659 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247659