Add native extensions for the Dart shell to mac and windows

runtime/bin/test_extension.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"
+#include "include/dart_api.h"
 
-#define EXPORT_SYMBOL __attribute__ ((visibility ("default")))
+Dart_NativeFunction ResolveName(Dart_Handle name, int argc);
 
-extern "C" Dart_NativeFunction ResolveName(Dart_Handle name, int argc);
+DART_EXPORT Dart_Handle test_extension_Init(Dart_Handle parent_library) {
+  if (Dart_IsError(parent_library)) { return parent_library; }
 
-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();
+  Dart_Handle result_code = Dart_SetNativeResolver(parent_library, ResolveName);
+  if (Dart_IsError(result_code)) return result_code;
+
+  return parent_library;
 }
 
-extern "C" void IfNull(Dart_NativeArguments arguments) {
+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) {
+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) {
+  if (!strcmp("TestExtension_IfNull", cname) && argc == 2) {
     return IfNull;
   }
   return NULL;
 }