Remove scanBuiltinLibraries.

tests/compiler/dart2js/mirrors/mirrors_test_helper.dart

 // Copyright (c) 2013, 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.
 
 import 'dart:io';
 import 'dart:async';
 
 import '../../../../sdk/lib/_internal/compiler/implementation/mirrors/source_mirrors.dart';
 import '../../../../sdk/lib/_internal/compiler/implementation/mirrors/analyze.dart' as source_mirrors;
 import '../../../../sdk/lib/_internal/compiler/implementation/source_file_provider.dart';
 
 TypeMirror createInstantiation(TypeSourceMirror type,
                                List<TypeMirror> typeArguments) {
   return type.createInstantiation(typeArguments);
 }
 
 Future<MirrorSystem> analyze(String test) {
   Uri repository = Platform.script.resolve('../../../../');
   Uri testUri = repository.resolve('tests/lib/mirrors/$test');
   return analyzeUri(testUri);
 }
 
 
 Future<MirrorSystem> analyzeUri(Uri testUri) {
   Uri repository = Platform.script.resolve('../../../../');
   Uri libraryRoot = repository.resolve('sdk/');
-  Uri packageRoot = Uri.base.resolve('${Platform.packageRoot}/');
+  Uri packageRoot = Uri.base.resolveUri(
+      new Uri.file('${Platform.packageRoot}/'));
   var provider = new CompilerSourceFileProvider();
   var handler = new FormattingDiagnosticHandler(provider);
   return source_mirrors.analyze(
       [testUri],
       libraryRoot,
       packageRoot,
       provider,
       handler);
 }