Dartdoc comments retrieved as metadata through dart2js mirrors.

tests/compiler/dart2js/mirrors_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 '../../../sdk/lib/_internal/compiler/implementation/mirrors/mirrors.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/mirrors/mirrors_util.dart';
 
 import 'dart:io';
 
 int count(Iterable iterable) {
@@ skipping 20 matching lines @@
     }
   }
   return null;
 }
 
 main() {
   var scriptPath = new Path.fromNative(new Options().script);
   var dirPath = scriptPath.directoryPath;
   var libPath = dirPath.join(new Path.fromNative('../../../sdk/'));
   var inputPath = dirPath.join(new Path.fromNative('mirrors_helper.dart'));
-  var compilation = new Compilation.library([inputPath], libPath);
+  var compilation = new Compilation.library([inputPath], libPath, null,
+      <String>['--preserve-comments']);
   Expect.isNotNull(compilation, "No compilation created");
 
   var mirrors = compilation.mirrors;
   Expect.isNotNull(mirrors, "No mirror system returned from compilation");
 
   var libraries = mirrors.libraries;
   Expect.isNotNull(libraries, "No libraries map returned");
   Expect.isFalse(libraries.isEmpty, "Empty libraries map returned");
 
   var helperLibrary = libraries["mirrors_helper"];
@@ skipping 885 matching lines @@
   Expect.isTrue(privateFactoryConstructor.isPrivate);
   Expect.isFalse(privateFactoryConstructor.isConstConstructor);
   Expect.isFalse(privateFactoryConstructor.isRedirectingConstructor);
   Expect.isFalse(privateFactoryConstructor.isGenerativeConstructor);
   Expect.isTrue(privateFactoryConstructor.isFactoryConstructor);
 
   var metadata = privateClass.metadata;
   Expect.isNotNull(metadata);
   Expect.equals(0, metadata.length);
 }