Move the Socket class to dedicated platform/socket.{cc,h} files.
Cleaned up the implementation to allow for more code sharing.

R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/23484014

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16521 ce2b1a6d-e550-0410-aec6-3dcde31c8c00