Initial 'Extract Local' implementation.

pkg/analysis_testing/lib/mock_sdk.dart

 // Copyright (c) 2014, 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 testing.mock_sdk;
 
 import 'package:analyzer/file_system/file_system.dart' as resource;
 import 'package:analyzer/file_system/memory_file_system.dart' as resource;
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/sdk.dart';
@@ skipping 14 matching lines @@
 class Symbol {}
 class Type {}
 
 abstract class Comparable<T> {
   int compareTo(T other);
 }
 
 class String implements Comparable<String> {
   bool get isEmpty => false;
   bool get isNotEmpty => false;
+  int get length => 0;
 }
 
 class bool extends Object {}
 abstract class num implements Comparable<num> {
   num operator +(num other);
   num operator -(num other);
   num operator *(num other);
   num operator /(num other);
   int toInt();
 }
@@ skipping 166 matching lines @@
   bool get isInternal => throw unimplemented;
 
   @override
   bool get isShared => throw unimplemented;
 
   @override
   bool get isVmLibrary => throw unimplemented;
 
   UnimplementedError get unimplemented => new UnimplementedError();
 }