Get rid of several old collection workarounds in serialization

pkg/serialization/lib/src/reader_writer.dart

Index: pkg/serialization/lib/src/reader_writer.dart
diff --git a/pkg/serialization/lib/src/reader_writer.dart b/pkg/serialization/lib/src/reader_writer.dart
index 920318555b2e00774d5aed8e74b81fb517f707e7..e99f9fb696529d0ae2ccafb70af8311d33c78f62 100644
--- a/pkg/serialization/lib/src/reader_writer.dart
+++ b/pkg/serialization/lib/src/reader_writer.dart
@@ -39,8 +39,8 @@ class Writer implements ReaderOrWriter {
    * once and stored here for each object. This provides some space-saving,
    * but also serves to record which objects we have already seen.
    */
-  final Map<dynamic, Reference> references =
-      new HashMap<Object, Reference>(equals: identical);
+  final Map<dynamic, Reference> references = 
+      new Map<Object, Reference>.identity();

[Jennifer Messerly, 2013/10/04 22:40:04]

This should stay as HashMap right? LinkedHashMap will cost performance in
exchange for being more deterministic. Normally the perf cost doesn't matter,
but serialization is one of the places where it might.

[Alan Knight, 2013/10/07 17:14:36]

Done.

 
   /**
    * The state of objects that need to be serialized is stored here.