Recognize unmodifiable lists

tests/compiler/dart2js/mock_libraries.dart

 // Copyright (c) 2014, 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.
 
 // Library for creating mock versions of platform and internal libraries.
 
 library mock_libraries;
 
 String buildLibrarySource(
     Map<String, String> elementMap,
@@ skipping 276 matching lines @@
       abstract class JSIndexable {
         get length;
         operator[](index);
       }''',
   'JSInt': r'''
        class JSInt extends JSNumber implements int {
          operator~() => this;
        }''',
   'JSMutableArray':
       'class JSMutableArray extends JSArray implements JSMutableIndexable {}',
+  'JSUnmodifiableArray':
+      'class JSUnmodifiableArray extends JSArray {}',
   'JSMutableIndexable':
       'abstract class JSMutableIndexable extends JSIndexable {}',
       'JSPositiveInt': 'class JSPositiveInt extends JSInt {}',
   'JSNull': r'''
       class JSNull extends Interceptor {
         bool operator==(other) => identical(null, other);
         get hashCode => throw "JSNull.hashCode not implemented.";
         String toString() => 'Null';
         Type get runtimeType => null;
         noSuchMethod(x) => super.noSuchMethod(x);
@@ skipping 74 matching lines @@
   'Stream': 'class Stream<T> {}',
   'Completer': 'class Completer<T> {}',
   'StreamIterator': 'class StreamIterator<T> {}',
 };
 
 const Map<String, String> DEFAULT_MIRRORS_LIBRARY = const <String, String>{
   'Comment': 'class Comment {}',
   'MirrorSystem': 'class MirrorSystem {}',
   'MirrorsUsed': 'class MirrorsUsed {}',
 };