Revert "Store actual Reference(s) for additional exports."

pkg/front_end/lib/src/fasta/kernel/kernel_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.kernel_library_builder;
 
+import 'dart:convert' show JSON;
+
 import 'package:front_end/src/fasta/combinator.dart' as fasta;
 import 'package:front_end/src/fasta/export.dart';
 import 'package:front_end/src/fasta/import.dart';
 import 'package:kernel/ast.dart';
 
 import 'package:kernel/clone.dart' show CloneVisitor;
 
 import '../../scanner/token.dart' show Token;
 
 import '../fasta_codes.dart'
@@ skipping 759 matching lines @@
       // TODO(scheglov): Add support for annotations, see
       // https://github.com/dart-lang/sdk/issues/30284.
       String fileUri = part.fileUri.toString();
       library.addPart(new LibraryPart(<Expression>[], fileUri));
     }
 
     library.name = name;
     library.procedures.sort(compareProcedures);
 
     if (additionalExports != null) {
-      library.additionalExports.addAll(additionalExports);
+      library.addMember(new Field(new Name("_exports#", library),
+          initializer: new StringLiteral(JSON.encode(additionalExports)),
+          isStatic: true,
+          isConst: true));
     }
 
     return library;
   }
 
   @override
   Builder buildAmbiguousBuilder(
       String name, Builder builder, Builder other, int charOffset,
       {bool isExport: false, bool isImport: false}) {
     // TODO(ahe): Can I move this to Scope or Prefix?
@@ skipping 153 matching lines @@
           mixinApplicationClasses.putIfAbsent(name, () => builder);
       if (existing != builder) {
         part.scope.local.remove(name);
       }
     });
     super.includePart(part);
     nativeMethods.addAll(part.nativeMethods);
     boundlessTypeVariables.addAll(part.boundlessTypeVariables);
   }
 }