Fix build bot error.

runtime/bin/extensions_macos.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 "platform/assert.h"
 #include "platform/globals.h"
 #if defined(TARGET_OS_MACOS)
 
 #include "bin/extensions.h"
 #include <dlfcn.h>  // NOLINT
 
 
 namespace dart {
 namespace bin {
 
 const char* kPrecompiledLibraryName = "libprecompiled.dylib";
 const char* kPrecompiledSymbolName = "kInstructionsSnapshot";
 
 Dart_Handle Extensions::LoadExtensionLibrary(const char* library_file,
                                              void** library_handle) {
   ASSERT(library_handle != NULL);
   *library_handle = dlopen(library_file, RTLD_LAZY);
   if (*library_handle == NULL) {
     return Dart_NewApiError(dlerror());
   }
   return Dart_Null();
 }
 
+void* Extensions::LoadExtensionLibrary(const char* library_file) {
+  return dlopen(library_file, RTLD_LAZY);
+}
+
 Dart_Handle Extensions::ResolveSymbol(void* lib_handle,
                                       const char* symbol,
                                       void** init_function) {
   ASSERT(init_function != NULL);
   dlerror();
   *init_function = dlsym(lib_handle, symbol);
   char* err_str = dlerror();
   if (err_str != NULL) {
     return Dart_NewApiError(err_str);
   }
   return Dart_Null();
 }
 
+void* Extensions::ResolveSymbol(void* lib_handle, const char* symbol) {
+  dlerror();
+  void* result = dlsym(lib_handle, symbol);
+  if (dlerror() != NULL) return NULL;
+  return result;
+}
+
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_MACOS)