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

pkg/front_end/test/fasta/ambiguous_export_test.dart

+// Copyright (c) 2017, 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.md file.
+
+import 'package:async_helper/async_helper.dart' show asyncTest;
+
+import 'package:expect/expect.dart' show Expect;
+
+import 'package:front_end/src/fasta/builder/builder.dart'
+    show InvalidTypeBuilder;
+
+import 'package:front_end/src/fasta/compiler_context.dart' show CompilerContext;
+
+import 'package:front_end/src/fasta/dill/dill_library_builder.dart'
+    show DillLibraryBuilder;
+
+import 'package:front_end/src/fasta/dill/dill_target.dart' show DillTarget;
+
+import 'package:kernel/ast.dart'
+    show Field, Library, Name, Program, StringLiteral;
+
+main() async {
+  await asyncTest(() async {
+    Library library = new Library(Uri.parse("org.dartlang.fasta:library"));
+    Field field = new Field(new Name("_exports#", library),
+        initializer:
+            new StringLiteral("[[null,\"main\",\"Problem with main\"]]"));
+    library.addMember(field);
+    Program program = new Program(libraries: <Library>[library]);
+    await CompilerContext.runWithDefaultOptions((CompilerContext c) async {
+      DillTarget target =
+          new DillTarget(c.options.ticker, null, c.options.target);
+      target.loader.appendLibraries(program);
+      DillLibraryBuilder builder = target.loader.read(library.importUri, -1);
+      await target.loader.buildOutline(builder);
+      builder.finalizeExports();
+      var mainExport = builder.exportScope.local["main"];
+      Expect.isTrue(mainExport is InvalidTypeBuilder);
+    });
+  });
+}