Implement fullNameForErrors on all Builders.

pkg/front_end/lib/src/fasta/builder/metadata_builder.dart

Index: pkg/front_end/lib/src/fasta/builder/metadata_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/builder/metadata_builder.dart b/pkg/front_end/lib/src/fasta/builder/metadata_builder.dart
index 02f9f1038f0223f9353ab25022901302b18c98ce..f8ae45b4bd8269f1cbded3f92b5bc35f3be9d208 100644
--- a/pkg/front_end/lib/src/fasta/builder/metadata_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/metadata_builder.dart
@@ -37,6 +37,9 @@ class ConstructorMetadataBuilder<T extends TypeBuilder>
   ConstructorMetadataBuilder(
       this.constructorReference, this.arguments, Builder parent, int charOffset)
       : super(parent, charOffset);
+
+  @override
+  String get fullNameForErrors => constructorReference.fullNameForErrors;
 }
 
 /// Expression metadata (without arguments).
@@ -53,4 +56,9 @@ class ExpressionMetadataBuilder<T extends TypeBuilder>
   ExpressionMetadataBuilder(
       this.qualified, this.identifier, Builder parent, int charOffset)
       : super(parent, charOffset);
+
+  @override
+  String get fullNameForErrors {
+    return identifier == null ? qualified : "$qualified.$identifier";
+  }
 }