WIP: Implement seccomp-bpf sandbox for nacl_helper_nonsfi.

components/nacl/loader/nacl_helper_linux.cc

Index: components/nacl/loader/nacl_helper_linux.cc
diff --git a/components/nacl/loader/nacl_helper_linux.cc b/components/nacl/loader/nacl_helper_linux.cc
index adb6d8b9c64abbdf563e149d10a588571d410b47..ae5f1aaf9db8a09973d3b5798d1c8e0555f7add9 100644
--- a/components/nacl/loader/nacl_helper_linux.cc
+++ b/components/nacl/loader/nacl_helper_linux.cc
@@ -108,11 +108,7 @@ void BecomeNaClLoader(base::ScopedFD browser_fd,
 
   // Finish layer-1 sandbox initialization and initialize the layer-2 sandbox.
   CHECK(!nacl_sandbox->HasOpenDirectory());
-#if !defined(OS_NACL_NONSFI)
-  // Currently Layer-two sandbox is not yet supported on nacl_helper_nonsfi.
-  // TODO(hidehiko): Enable the sandbox.
   nacl_sandbox->InitializeLayerTwoSandbox(uses_nonsfi_mode);
-#endif
   nacl_sandbox->SealLayerOneSandbox();
   nacl_sandbox->CheckSandboxingStateWithPolicy();