Implement automatic loading of dart:core_native_fields library

bin/dartutils.h

 // Copyright (c) 2011, 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.
 
 #ifndef BIN_DARTUTILS_H_
 #define BIN_DARTUTILS_H_
 
 #include "bin/builtin.h"
 #include "bin/globals.h"
 
 #include "include/dart_api.h"
 
 class DartUtils {
  public:
   static int64_t GetIntegerValue(Dart_Handle value_obj);
   static const char* GetStringValue(Dart_Handle str_obj);
   static bool GetBooleanValue(Dart_Handle bool_obj);
   static void SetIntegerInstanceField(Dart_Handle handle,
                                       const char* name,
                                       intptr_t val);
   static intptr_t GetIntegerInstanceField(Dart_Handle handle,
                                           const char* name);
   static void SetStringInstanceField(Dart_Handle handle,
                                      const char* name,
                                      const char* val);
 
   static const char* kBuiltinLibURL;
-  static const char* kBuiltinLibSpec;
+  static const char* kCoreLibURL;
+  static const char* kCoreImplLibURL;
+  static const char* kCoreNativeWrappersLibURL;
 
   static const char* kIdFieldName;
  private:
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(DartUtils);
 };
 
 #endif  // BIN_DARTUTILS_H_