Set fileUri when creating library builders.

pkg/front_end/lib/src/fasta/dill/dill_target.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.dill_target;
 
 import 'dart:async' show
     Future;
 
 import 'package:kernel/ast.dart' show
@@ skipping 46 matching lines @@
     return internalError("not implemented.");
   }
 
   Future<Null> writeOutline(Uri uri) async {
     if (loader.input == null) return null;
     await loader.buildOutlines();
     isLoaded = true;
     return null;
   }
 
-  DillLibraryBuilder createLibraryBuilder(Uri uri) {
+  DillLibraryBuilder createLibraryBuilder(Uri uri, Uri fileUri) {
     return new DillLibraryBuilder(uri, loader);
   }
 
   void addDirectSupertype(ClassBuilder cls, Set<ClassBuilder> set) {
   }
 
   List<ClassBuilder> collectAllClasses() {
     return null;
   }
 
   void breakCycle(ClassBuilder cls) {
   }
 
   Class get objectClass {
     KernelClassBuilder builder = loader.coreLibrary.exports["Object"];
     return builder.cls;
   }
 }