Revert "Remove Registry from registerMetadataConstant" and "Serialize metadata"

pkg/compiler/lib/src/parser/element_listener.dart

Index: pkg/compiler/lib/src/parser/element_listener.dart
diff --git a/pkg/compiler/lib/src/parser/element_listener.dart b/pkg/compiler/lib/src/parser/element_listener.dart
index 6d9bd8252a9f9045a0b83bd4c2544a3da0928e1b..6fe019cdae5ac31f2f075df7d495fc19a1d0c238 100644
--- a/pkg/compiler/lib/src/parser/element_listener.dart
+++ b/pkg/compiler/lib/src/parser/element_listener.dart
@@ -17,7 +17,6 @@ import '../elements/modelx.dart'
         EnumClassElementX,
         FieldElementX,
         LibraryElementX,
-        MetadataAnnotationX,
         NamedMixinApplicationElementX,
         VariableList;
 import '../id_generator.dart';
@@ -234,8 +233,8 @@ class ElementListener extends Listener {
 
   void endTopLevelDeclaration(Token token) {
     if (!metadata.isEmpty) {
-      MetadataAnnotationX first = metadata.first;
-      recoverableError(first.beginToken, 'Metadata not supported here.');
+      recoverableError(
+          metadata.first.beginToken, 'Metadata not supported here.');
       metadata.clear();
     }
   }