anchor.diff:        : enclosingScope = scope,
           library = library,
           enableNative = library.loader.target.enableNative(library),
  -        isPlatformLibrary = library.uri.scheme == 'dart',
  +        isBuiltinLibrary =
  +            library.uri.scheme == 'dart' && library.uri.path == "_builtin",
           needsImplicitSuperInitializer =
               coreTypes.objectClass != classBuilder?.cls,
           typePromoter = _typeInferrer.typePromoter,
  
positive.code:           return new UnresolvedAccessor(this, n, token);
          }
          return new ThisPropertyAccessor(this, token, n, null, null);
        } else if (
            // Optimization, if [isPlatformLibrary] is false, this can't be
            // dart:_builtin.
            isPlatformLibrary &&
                name == "main" &&
                library.uri.path == "_builtin" &&
                member?.name == "_getMainClosure") {
          // TODO(ahe): https://github.com/dart-lang/sdk/issues/28989
          return new KernelNullLiteral()..fileOffset = offsetForToken(token);
        } else {
  
negative.code: 
    final bool enableNative;
  
    final bool isBuiltinLibrary;
  
    @override
    final Uri uri;
  