Ensure locations are always provided, but don't store them yet.

pkg/front_end/lib/src/fasta/builder/constructor_reference_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.constructor_reference_builder;
 
 import 'builder.dart' show
     PrefixBuilder,
     ClassBuilder,
     Builder,
     TypeBuilder;
 
 import 'scope.dart' show
     Scope;
 
 class ConstructorReferenceBuilder extends Builder {
   final String name;
 
   final List<TypeBuilder> typeArguments;
 
   /// This is the name of a named constructor. As `bar` in `new Foo<T>.bar()`.
   final String suffix;
 
   Builder target;
 
-  ConstructorReferenceBuilder(this.name, this.typeArguments, this.suffix);
+  ConstructorReferenceBuilder(this.name, this.typeArguments, this.suffix,
+      Builder parent, int charOffset)
+      : super(parent, charOffset, parent.fileUri);
 
   String get fullNameForErrors => "$name${suffix == null ? '' : '.$suffix'}";
 
   void resolveIn(Scope scope) {
     int index = name.indexOf(".");
     Builder builder;
     if (index == -1) {
-      builder = scope.lookup(name);
+      builder = scope.lookup(name, charOffset, fileUri);
     } else {
       String prefix = name.substring(0, index);
       String middle = name.substring(index + 1);
-      builder = scope.lookup(prefix);
+      builder = scope.lookup(prefix, charOffset, fileUri);
       if (builder is PrefixBuilder) {
         PrefixBuilder prefix = builder;
         builder = prefix.exports[middle];
       } else if (builder is ClassBuilder) {
         ClassBuilder cls = builder;
         builder = cls.constructors[middle];
         if (suffix == null) {
           target = builder;
           return;
         }
       }
     }
     if (builder is ClassBuilder) {
       target = builder.constructors[suffix ?? ""];
     }
     if (target == null) {
       print("Couldn't find constructor $fullNameForErrors.");
     }
   }
 }