Use UnmodifiableMapView in compiler

sdk/lib/_internal/compiler/implementation/mirrors/util.dart

Index: sdk/lib/_internal/compiler/implementation/mirrors/util.dart
diff --git a/sdk/lib/_internal/compiler/implementation/mirrors/util.dart b/sdk/lib/_internal/compiler/implementation/mirrors/util.dart
index 2ea4638c6b9d0647c5ab191bc3ce1e10f546e0fe..7f505dbdb30793961e6fa8283e424a4a4cd2dced 100644
--- a/sdk/lib/_internal/compiler/implementation/mirrors/util.dart
+++ b/sdk/lib/_internal/compiler/implementation/mirrors/util.dart
@@ -135,50 +135,3 @@ class FilteredImmutableMap<K, V> extends ImmutableMapWrapper<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);
-      }
-    });
-  }
-}