Reapply change to hide VM-only List implementation classes.

runtime/lib/immutable_map.dart

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// 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.
 // Immutable map class for compiler generated map literals.
 
 class ImmutableMap<K, V> implements Map<K, V> {
-  final ImmutableArray kvPairs_;
+  final _ImmutableArray kvPairs_;
 
-  const ImmutableMap._create(ImmutableArray keyValuePairs)
+  const ImmutableMap._create(_ImmutableArray keyValuePairs)
       : kvPairs_ = keyValuePairs;
 
 
   V operator [](K key) {
     // TODO(hausner): Since the keys are sorted, we could do a binary
     // search. But is it worth it?
     for (int i = 0; i < kvPairs_.length - 1; i += 2) {
       if (key == kvPairs_[i]) {
         return kvPairs_[i+1];
       }
@@ skipping 65 matching lines @@
 
   V remove(K key) {
     throw const IllegalAccessException();
   }
 
   String toString() {
     return Maps.mapToString(this);
   }
 }