Reduce usage of ItearbleMixinWorkaround.

pkg/serialization/lib/src/serialization_rule.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.
 
 part of serialization;
 
 // TODO(alanknight): We should have an example and tests for subclassing
 // serialization rule rather than using the hard-coded ClosureToMap rule. And
 // possibly an abstract superclass that's designed to be subclassed that way.
 /**
@@ skipping 526 matching lines @@
 
   // These operations, and other inherited methods that iterate over the whole
   // list will work, but may be expensive, and are probably
   // best avoided.
   List get _inflated => _raw.map(_reader.inflateReference);
   Iterator get iterator => _inflated.iterator;
   indexOf(x, [pos = 0]) => _inflated.toList().indexOf(x);
   lastIndexOf(x, [pos]) => _inflated.toList().lastIndexOf(x);
   sublist(start, [end]) => _inflated.sublist(start, end);
 
-  Map<int, dynamic> asMap() => IterableMixinWorkaround.asMapList(this);
+  Map<int, dynamic> asMap() => _inflated.asMap();
 
   // These operations are all invalid
   _throw() {
     throw new UnsupportedError("Not modifiable");
   }
   operator []=(x, y) => _throw();
   add(x) => _throw();
   addAll(x) => _throw();
   sort([f]) => _throw();
   clear() => _throw();
   insert(x, y) => _throw();
   removeAt(x) => _throw();
   remove(x) => _throw();
   removeLast() => _throw();
   removeAll(x) => _throw();
   retainAll(x) => _throw();
   removeWhere(x) => _throw();
   retainWhere(x) => _throw();
   getRange(x, y) => _throw();
   setRange(x, y, z, [a]) => _throw();
   removeRange(x, y) => _throw();
   insertRange(x, y, [z]) => _throw();
   get reversed => _throw();
   void set length(x) => _throw();
 }