Implement fullNameForErrors on all Builders.

pkg/front_end/lib/src/fasta/source/source_library_builder.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library fasta.source_library_builder;
 
 import 'package:kernel/ast.dart' show AsyncMarker, ProcedureKind;
 
 import '../combinator.dart' show Combinator;
 
@@ skipping 424 matching lines @@
   int resolveConstructors(_) {
     int count = 0;
     members.forEach((String name, Builder member) {
       count += member.resolveConstructors(this);
     });
     return count;
   }
 
   List<TypeVariableBuilder> copyTypeVariables(
       List<TypeVariableBuilder> original);
+
+  @override
+  String get fullNameForErrors => name ?? "<library '$relativeFileUri'>";
 }
 
 /// Unlike [Scope], this scope is used during construction of builders to
 /// ensure types and members are added to and resolved in the correct location.
 class DeclarationBuilder<T extends TypeBuilder> {
   final DeclarationBuilder<T> parent;
 
   final Map<String, Builder> members;
 
   final List<T> types = <T>[];
@@ skipping 65 matching lines @@
   }
 
   /// Called to register [procedure] as a factory whose types are collected in
   /// [factoryDeclaration]. Later, once the class has been built, we can
   /// synthesize type variables on the factory matching the class'.
   void addFactoryDeclaration(
       ProcedureBuilder procedure, DeclarationBuilder<T> factoryDeclaration) {
     factoryDeclarations[procedure] = factoryDeclaration;
   }
 }