Add Iterable type to mock SDK for analyzer2dart.

pkg/analyzer2dart/test/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 40 matching lines @@
 class double extends num {}
 class DateTime extends Object {}
 class Null extends Object {}
 
 class Deprecated extends Object {
   final String expires;
   const Deprecated(this.expires);
 }
 const Object deprecated = const Deprecated("next release");
 
-abstract class List<E> extends Object {
+abstract class Iterable<E> {}
+
+abstract class List<E> extends Object implements Iterable {
   void add(E value);
   E operator [](int index);
   void operator []=(int index, E value);
 }
 class Map<K, V> extends Object {}
 
 external bool identical(Object a, Object b);
 
 void print(Object object) {}
 
@@ skipping 167 matching lines @@
   bool get isInternal => throw unimplemented;
 
   @override
   bool get isShared => throw unimplemented;
 
   @override
   bool get isVmLibrary => throw unimplemented;
 
   UnimplementedError get unimplemented => new UnimplementedError();
 }