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

pkg/compiler/lib/src/constants/values.dart

Index: pkg/compiler/lib/src/constants/values.dart
diff --git a/pkg/compiler/lib/src/constants/values.dart b/pkg/compiler/lib/src/constants/values.dart
index 670d1efde88f7e6040d7177b6bb1a62520f8851c..37f5646d7e3600f22f575df233d3153b2273f62e 100644
--- a/pkg/compiler/lib/src/constants/values.dart
+++ b/pkg/compiler/lib/src/constants/values.dart
@@ -28,7 +28,6 @@ abstract class ConstantValueVisitor<R, A> {
   R visitInterceptor(InterceptorConstantValue constant, A arg);
   R visitSynthetic(SyntheticConstantValue constant, A arg);
   R visitDeferred(DeferredConstantValue constant, A arg);
-  R visitNonConstant(NonConstantValue constant, A arg);
 }
 
 abstract class ConstantValue {
@@ -763,7 +762,7 @@ class NonConstantValue extends ConstantValue {
 
   @override
   accept(ConstantValueVisitor visitor, arg) {
-    return visitor.visitNonConstant(this, arg);
+    // TODO(johnniwinther): Should this be part of the visiting?
   }
 
   @override