Get rid of several old collection workarounds in serialization

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 517 matching lines @@
   operator [](x) => _reader.inflateReference(_raw[x]);
 
   int get length => _raw.length;
   bool get isEmpty => _raw.isEmpty;
   bool get isNotEmpty => _raw.isNotEmpty;
   Iterable get keys => _raw.keys;
   bool containsKey(x) => _raw.containsKey(x);
 
   // These operations will work, but may be expensive, and are probably
   // best avoided.
-  get _inflated => keysAndValues(_raw).map(_reader.inflateReference);
+  get _inflated => mapValues(_raw, _reader.inflateReference);
   bool containsValue(x) => _inflated.containsValue(x);
   Iterable get values => _inflated.values;
   void forEach(f) => _inflated.forEach(f);
 
   // These operations are all invalid
   _throw() {
     throw new UnsupportedError("Not modifiable");
   }
   operator []=(x, y) => _throw();
   putIfAbsent(x, y) => _throw();
@@ skipping 19 matching lines @@
   int get length => _raw.length;
 
   void set length(int value) => _throw();
 
   void operator []=(int index, value) => _throw();
 
   void _throw() {
     throw new UnsupportedError("Not modifiable");
   }
 }