Add native extensions for the Dart shell to mac and windows

runtime/bin/test_extension_linux.cc

-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
-// 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.
-
-#include <string.h>
-
-#include "../include/dart_api.h"
-
-#define EXPORT_SYMBOL __attribute__ ((visibility ("default")))
-
-extern "C" Dart_NativeFunction ResolveName(Dart_Handle name, int argc);
-
-extern "C" EXPORT_SYMBOL Dart_Handle test_extension_Init(Dart_Handle library) {
-  if (Dart_IsError(library)) return library;
-  Dart_Handle check_return = Dart_SetNativeResolver(library, ResolveName);
-  if (Dart_IsError(check_return)) return check_return;
-  return Dart_Null();
-}
-
-extern "C" void IfNull(Dart_NativeArguments arguments) {
-  Dart_Handle object = Dart_GetNativeArgument(arguments, 0);
-  if (Dart_IsNull(object)) {
-    Dart_SetReturnValue(arguments, Dart_GetNativeArgument(arguments, 1));
-  } else {
-    Dart_SetReturnValue(arguments, object);
-  }
-}
-
-extern "C" Dart_NativeFunction ResolveName(Dart_Handle name, int argc) {
-  assert(Dart_IsString8(name));
-  const char* cname;
-  Dart_Handle check_error;
-
-  check_error = Dart_StringToCString(name, &cname);
-  if (Dart_IsError(check_error)) {
-    Dart_PropagateError(check_error);
-  }
-  if (!strcmp("Cat_IfNull", cname) && argc == 2) {
-    return IfNull;
-  }
-  return NULL;
-}