- Reverting mirror changes.

pkg/serialization/lib/src/serialization_rule.dart

Index: pkg/serialization/lib/src/serialization_rule.dart
===================================================================
--- pkg/serialization/lib/src/serialization_rule.dart	(revision 30026)
+++ pkg/serialization/lib/src/serialization_rule.dart	(working copy)
@@ -410,13 +410,18 @@
     if (name.contains(":")) {
       var uri = Uri.parse(name);
       var libMirror = currentMirrorSystem().libraries[uri];
-      return libMirror.classes[new Symbol(type)];
+      var result = libMirror.declarations[new Symbol(type)];
+      return result is ClassMirror ? result : null;
     } else {
       var symbol = new Symbol(name);
       var typeSymbol = new Symbol(type);
-      var libMirror = currentMirrorSystem().libraries.values.firstWhere(
-        (lib) => lib.simpleName == symbol && lib.classes[typeSymbol] != null);
-      return libMirror.classes[typeSymbol];
+      var libMirror = currentMirrorSystem().libraries.values.firstWhere((lib) {
+        if (lib.simpleName != symbol) return false;
+        var candidate = lib.declarations[typeSymbol];
+        return candidate != null && candidate is ClassMirror;
+      });
+      var result = libMirror.declarations[typeSymbol];
+      return result is ClassMirror ? result : null;
     }
   }
 }