GitLab

This is a pre-requisite for http server refactoring,
https://codereview.chromium.org/296053012/.

1) Define UnixDomainClientSocket and UnixDomainServerSocket utilizing
   SocketLibevent.
2) Rename UnixDomainSocket to UnixDomainListenSocket to reduce confusion.
3) unittests

BUG=371906

Review URL: https://codereview.chromium.org/376323002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@285148 0039d316-1c4b-4281-b951-d872f2087c98