Add SandboxBPFPolicy::InvalidSyscall() to simplify writing policies

sandbox/linux/seccomp-bpf/sandbox_bpf_policy.cc

+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "sandbox/linux/seccomp-bpf/sandbox_bpf_policy.h"
+
+#include <errno.h>
+
+#include "sandbox/linux/seccomp-bpf/errorcode.h"
+
+namespace sandbox {
+
+ErrorCode SandboxBPFPolicy::InvalidSyscall(SandboxBPF* sandbox_compiler) const {
+  return ErrorCode(ENOSYS);
+}
+
+}  // namespace sandbox