Add reusePort argument to ServerSocket.

runtime/bin/socket.cc

Index: runtime/bin/socket.cc
diff --git a/runtime/bin/socket.cc b/runtime/bin/socket.cc
index 4dfbe503fa750f586c45091acb6e6cc59950c660..02fa3921af1058c4a985796fdac19a57c5120ac1 100644
--- a/runtime/bin/socket.cc
+++ b/runtime/bin/socket.cc
@@ -302,14 +302,16 @@ void FUNCTION_NAME(ServerSocket_CreateBindListen)(Dart_NativeArguments args) {
   Dart_Handle port_obj = Dart_GetNativeArgument(args, 2);
   Dart_Handle backlog_obj = Dart_GetNativeArgument(args, 3);
   Dart_Handle v6_only_obj = Dart_GetNativeArgument(args, 4);
+  Dart_Handle reuse_port_obj = Dart_GetNativeArgument(args, 5);
   bool v6_only = DartUtils::GetBooleanValue(v6_only_obj);
+  bool reuse_port = DartUtils::GetBooleanValue(reuse_port_obj);
   int64_t port = 0;
   int64_t backlog = 0;
   if (!Dart_IsError(result) &&
       DartUtils::GetInt64Value(port_obj, &port) &&
       DartUtils::GetInt64Value(backlog_obj, &backlog)) {
     intptr_t socket = ServerSocket::CreateBindListen(
-        addr, port, backlog, v6_only);
+        addr, port, backlog, v6_only, reuse_port);
     OSError error;
     Dart_TypedDataReleaseData(host_obj);
     if (socket >= 0) {