Change MirrorSystem.libraries to Map<Uri, String>

tests/compiler/dart2js/mirrors_metadata_test.dart

 // 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.
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:uri';
+import 'package:expect/expect.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/filenames.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/mirrors/mirrors.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/mirrors/dart2js_mirror.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/source_file_provider.dart';
 import 'mock_compiler.dart';
 
 const String SOURCE = 'source';
+const Uri SOURCE_URI = const Uri.fromComponents(scheme: SOURCE, path: SOURCE);
 
 MirrorSystem createMirrorSystem(String source) {
-  Uri sourceUri = new Uri.fromComponents(scheme: SOURCE, path: SOURCE);
   MockCompiler compiler = new MockCompiler(
       analyzeOnly: true,
       analyzeAll: true,
       preserveComments: true);
-  compiler.registerSource(sourceUri, source);
-  compiler.librariesToAnalyzeWhenRun = <Uri>[sourceUri];
+  compiler.registerSource(SOURCE_URI, source);
+  compiler.librariesToAnalyzeWhenRun = <Uri>[SOURCE_URI];
   compiler.runCompiler(null);
   return new Dart2JsMirrorSystem(compiler);
 }
 
 void validateDeclarationComment(String code,
                                 String text,
                                 String trimmedText,
                                 bool isDocComment,
                                 List<String> declarationNames) {
   MirrorSystem mirrors = createMirrorSystem(code);
-  LibraryMirror library = mirrors.libraries[SOURCE];
+  LibraryMirror library = mirrors.libraries[SOURCE_URI];
   Expect.isNotNull(library);
   for (String declarationName in declarationNames) {
     DeclarationMirror declaration = library.members[declarationName];
     Expect.isNotNull(declaration);
     List<InstanceMirror> metadata = declaration.metadata;
     Expect.isNotNull(metadata);
     Expect.equals(1, metadata.length);
     Expect.isTrue(metadata[0] is CommentInstanceMirror);
     CommentInstanceMirror commentMetadata = metadata[0];
     Expect.equals(text, commentMetadata.text);
@@ skipping 31 matching lines @@
   testDeclarationComment('final int field = 0;', ['field']);
   testDeclarationComment('final field1 = 0, field2 = 0;', ['field1', 'field2']);
   testDeclarationComment('final int field1 = 0, field2 = 0;',
                          ['field1', 'field2']);
   testDeclarationComment('const field = 0;', ['field']);
   testDeclarationComment('const int field = 0;', ['field']);
   testDeclarationComment('const field1 = 0, field2 = 0;', ['field1', 'field2']);
   testDeclarationComment('const int field1 = 0, field2 = 0;',
                          ['field1', 'field2']);
 }