Update pkg/serialization to use Symbols and synchronous mirrors

pkg/serialization/lib/serialization.dart

Index: pkg/serialization/lib/serialization.dart
diff --git a/pkg/serialization/lib/serialization.dart b/pkg/serialization/lib/serialization.dart
index 130be2741fa33dfd53dfdbeb26d59927353a605c..eca8bfbf5f2b6ede1b00a209100cf1bbfa1a30a2 100644
--- a/pkg/serialization/lib/serialization.dart
+++ b/pkg/serialization/lib/serialization.dart
@@ -319,6 +319,7 @@ class Serialization {
     // it will always find the first one.
     addRule(new ListRuleEssential());
     addRule(new MapRule());
+    addRule(new SymbolRule());
   }
 
   /**
@@ -445,7 +446,8 @@ class Serialization {
             'constructorFields', 'regularFields', []],
           fields: [])
       ..addRule(new NamedObjectRule())
-      ..addRule(new MirrorRule());
+      ..addRule(new MirrorRule())
+      ..addRule(new SymbolRule());
     meta.namedObjects = namedObjects;
     return meta;
   }