Implement CompilationUnitElement.lineInfo in MockCompilationUnitElement.

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/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 
 import '../builder/builder.dart' show
     Builder;
 
 import '../errors.dart' show
     internalError;
+import 'package:analyzer/src/generated/source.dart';
 
 abstract class MockElement extends Builder
     implements Element, LocalElement {
   final ElementKind kind;
 
   MockElement(this.kind)
       : super(null, -1, null);
 
   get librarySource => internalError("not supported.");
 
@@ skipping 178 matching lines @@
   List<ClassElement> get enums => internalError("not supported.");
 
   List<FunctionElement> get functions => internalError("not supported.");
 
   List<FunctionTypeAliasElement> get functionTypeAliases {
     return internalError("not supported.");
   }
 
   bool get hasLoadLibraryFunction => internalError("not supported.");
 
+  @override
+  LineInfo get lineInfo => internalError("not supported.");
+
   List<TopLevelVariableElement> get topLevelVariables {
     return internalError("not supported.");
   }
 
   List<ClassElement> get types => internalError("not supported.");
 
   Element getElementAt(int offset) => internalError("not supported.");
 
   ClassElement getEnum(String name) => internalError("not supported.");
 
@@ skipping 147 matching lines @@
   get constantValue => internalError("not supported.");
 
   computeConstantValue() => internalError("not supported.");
 
   void appendToWithoutDelimiters(StringBuffer buffer) {
     return internalError("not supported.");
   }
 
   FormalParameter computeNode() => internalError("not supported.");
 }