Fix a style nit in client_socket.h.

Use the |os_error| name consistently for all the function
arguments and local variables that represent OS errors.

R=eroman
BUG=none
TEST=none
Review URL: http://codereview.chromium.org/374008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@31537 0039d316-1c4b-4281-b951-d872f2087c98

• net/socket/client_socket.h[diff]
• net/socket/tcp_client_socket_libevent.cc[diff]
• net/socket/tcp_client_socket_win.cc[diff]