Renamed RemotingDirectoryService to DirectoryAddRequest. It will be used in RemotingSetupFlow to register host. Also added unittests for this code.

BUG=67218
TEST=Unittests

Review URL: http://codereview.chromium.org/6036001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@70082 0039d316-1c4b-4281-b951-d872f2087c98