Reduce header dependencies in net/

TEST=none

Review URL: http://codereview.chromium.org/115870

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@17178 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/net/base/tcp_client_socket_libevent.cc b/net/base/tcp_client_socket_libevent.cc
index e011100..7d42e4a 100644
--- a/net/base/tcp_client_socket_libevent.cc
+++ b/net/base/tcp_client_socket_libevent.cc
@@ -13,6 +13,7 @@
 #include "base/message_loop.h"
 #include "base/string_util.h"
 #include "base/trace_event.h"
+#include "net/base/io_buffer.h"
 #include "net/base/net_errors.h"
 #include "third_party/libevent/event.h"