Re-land socket refactor with fixes for Windows.

runtime/bin/socket_base_fuchsia.h

Index: runtime/bin/socket_base_fuchsia.h
diff --git a/runtime/bin/socket_fuchsia.h b/runtime/bin/socket_base_fuchsia.h
similarity index 54%
rename from runtime/bin/socket_fuchsia.h
rename to runtime/bin/socket_base_fuchsia.h
index a19df5dd8eac3b7fb00870a0ddd880e1ea257575..3ec33432202c8b0577357d4bb90e2dc9bc44eb8c 100644
--- a/runtime/bin/socket_fuchsia.h
+++ b/runtime/bin/socket_base_fuchsia.h
@@ -2,15 +2,15 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-#ifndef RUNTIME_BIN_SOCKET_FUCHSIA_H_
-#define RUNTIME_BIN_SOCKET_FUCHSIA_H_
+#ifndef RUNTIME_BIN_SOCKET_BASE_FUCHSIA_H_
+#define RUNTIME_BIN_SOCKET_BASE_FUCHSIA_H_
 
-#if !defined(RUNTIME_BIN_SOCKET_H_)
-#error Do not include socket_fuchsia.h directly. Use socket.h.
+#if !defined(RUNTIME_BIN_SOCKET_BASE_H_)
+#error Do not include socket_base_fuchsia.h directly. Use socket_base.h.
 #endif
 
 #include <arpa/inet.h>
 #include <netdb.h>
 #include <sys/socket.h>
 
-#endif  // RUNTIME_BIN_SOCKET_FUCHSIA_H_
+#endif  // RUNTIME_BIN_SOCKET_BASE_FUCHSIA_H_