Use UnmodifiableMapView in compiler

sdk/lib/_internal/compiler/implementation/mirrors/util.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.
 
 library dart2js.mirrors.util;
 
 import 'dart:collection' show Maps;
 
 /**
  * An abstract map implementation. This class can be used as a superclass for
@@ skipping 117 matching lines @@
   }
 
   void forEach(void f(K key, V value)) {
     _map.forEach((K k, V v) {
       if (_filter(v)) {
         f(k, v);
       }
     });
   }
 }
-
-/**
- * An [AsFilter] takes a [value] of type [V1] and returns [value] iff it is of
- * type [V2] or [:null:] otherwise. An [AsFilter] therefore behaves like the
- * [:as:] expression.
- */
-typedef V2 AsFilter<V1, V2>(V1 value);
-
-/**
- * An immutable map wrapper capable of filtering the input map based on types.
- * It takes an [AsFilter] function which converts the original values of type
- * [Vin] into values of type [Vout], or returns [:null:] if the value should
- * not be included in the filtered map.
- */
-class AsFilteredImmutableMap<K, Vin, Vout> extends AbstractMap<K, Vout> {
-  final Map<K, Vin> _map;
-  final AsFilter<Vin, Vout> _filter;
-
-  AsFilteredImmutableMap(this._map, this._filter);
-
-  int get length {
-    var count = 0;
-    forEach((k,v) {
-      count++;
-    });
-    return count;
-  }
-
-  Vout operator [](K key) {
-    if (key is K) {
-      Vin value = _map[key];
-      if (value != null) {
-        return _filter(value);
-      }
-    }
-    return null;
-  }
-
-  void forEach(void f(K key, Vout value)) {
-    _map.forEach((K k, Vin v) {
-      var value = _filter(v);
-      if (value != null) {
-        f(k, value);
-      }
-    });
-  }
-}