Set fileUri when creating library builders.

pkg/front_end/lib/src/fasta/dill/dill_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.dill_library_builder;
 
 import 'package:kernel/ast.dart' show
     Class,
     ExpressionStatement,
     Field,
@@ skipping 35 matching lines @@
   final Map<String, Builder> exports = <String, Builder>{};
 
   final DillLoader loader;
 
   Library library;
 
   DillLibraryBuilder(this.uri, this.loader);
 
   get scope => internalError("Scope not supported");
 
+  Uri get fileUri => uri;
+
   void addClass(Class cls) {
     DillClassBuilder classBulder = new DillClassBuilder(cls, this);
     addBuilder(cls.name, classBulder);
     cls.procedures.forEach(classBulder.addMember);
     cls.constructors.forEach(classBulder.addMember);
     for (Field field in cls.fields) {
       if (field.name.name == "_redirecting#") {
         // This is a hack / work around for storing redirecting constructors in
         // dill files. See `buildFactoryConstructor` in
         // [package:kernel/analyzer/ast_from_analyzer.dart]
@@ skipping 41 matching lines @@
 
   void addToScope(String name, Builder member) {
     internalError("Not implemented yet.");
   }
 
   KernelInvalidTypeBuilder buildAmbiguousBuilder(
       String name, Builder builder, Builder other) {
     return new KernelInvalidTypeBuilder(name, this);
   }
 }