Add NetworkingPrivateDelegate class
This CL introduces NetworkingPrivateDelegate and moves (almost) all extension API specific code into a common NetworkingPrivateApi class.
The ChromeOS specific Delegate is now in networking_private_api_chromeos.cc (now a profile keyed service).
The Windows/Mac specific Delegate is now in networking_private_service_client.cc. networking_private_api_nonchromeos.cc has been deleted.
BUG=392708
Review URL: https://codereview.chromium.org/
378103002
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@284019 0039d316-1c4b-4281-b951-d872f2087c98