Handle complicated imports.

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

Index: pkg/front_end/lib/src/fasta/builder/invalid_type_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/builder/invalid_type_builder.dart b/pkg/front_end/lib/src/fasta/builder/invalid_type_builder.dart
index b17457099e819e456a4897f299015f8cccee32f0..5b646010d4631fdbafe606ed906501c55388622f 100644
--- a/pkg/front_end/lib/src/fasta/builder/invalid_type_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/invalid_type_builder.dart
@@ -4,16 +4,10 @@
 
 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;
-  }
 }