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

pkg/front_end/lib/src/fasta/analyzer/mock_element.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.analyzer.mock_element;
 
 import 'package:analyzer/dart/element/element.dart';
 
+import '../builder/builder.dart' show
+    Builder;
+
 import '../errors.dart' show
     internalError;
 
-abstract class MockElement implements Element {
+abstract class MockElement extends Builder implements Element {
   final ElementKind kind;
 
-  MockElement(this.kind);
+  MockElement(this.kind)
+      : super(null, -1, null);
 
   get librarySource => internalError("not supported.");
 
   get source => internalError("not supported.");
 
   get context => internalError("not supported.");
 
   String get displayName => internalError("not supported.");
 
   String get documentationComment => internalError("not supported.");
@@ skipping 325 matching lines @@
   List<ParameterElement> get parameters => internalError("not supported.");
 
   List<TypeParameterElement> get typeParameters {
     return internalError("not supported.");
   }
 
   void appendToWithoutDelimiters(StringBuffer buffer) {
     return internalError("not supported.");
   }
 }