Handle complicated imports.

pkg/front_end/lib/src/fasta/builder/invalid_type_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.invalid_type_builder;
 
-import 'builder.dart'
-    show Builder, LibraryBuilder, TypeBuilder, TypeDeclarationBuilder;
+import 'builder.dart' show TypeBuilder, TypeDeclarationBuilder;
 
 abstract class InvalidTypeBuilder<T extends TypeBuilder, R>
     extends TypeDeclarationBuilder<T, R> {
   InvalidTypeBuilder(String name, int charOffset, [Uri fileUri])
       : super(null, 0, name, null, charOffset, fileUri);
-
-  Builder combineAmbiguousImport(
-      String name, Builder other, LibraryBuilder library) {
-    return this;
-  }
 }