Add warnings and hints to for-in.

tests/compiler/dart2js/mock_libraries.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 for creating mock versions of platform and internal libraries.
 
 library mock_libraries;
 
 String buildLibrarySource(
     Map<String, String> elementMap,
@@ skipping 27 matching lines @@
       abstract class double extends num {
         static var NAN = 0;
         static parse(s) {}
       }''',
   'Function': r'''
       class Function {
         static apply(Function fn, List positional, [Map named]) => null;
       }''',
   'identical': 'bool identical(Object a, Object b) { return true; }',
   'int': 'abstract class int extends num { }',
-  'Iterable': 'abstract class Iterable {}',
+  'Iterable': '''
+      abstract class Iterable<E> {
+          Iterator<E> get iterator => null;
+      }''',
+  'Iterator': '''
+      abstract class Iterator<E> {
+          E get current => null;
+      }''',
   'LinkedHashMap': r'''
       class LinkedHashMap {
         factory LinkedHashMap._empty() => null;
         factory LinkedHashMap._literal(elements) => null;
         static _makeEmpty() => null;
         static _makeLiteral(elements) => null;
       }''',
   'List': r'''
-      class List<E> {
+      class List<E> extends Iterable<E> {
         var length;
         List([length]);
         List.filled(length, element);
         E get first => null;
         E get last => null;
         E get single => null;
         E removeLast() => null;
         E removeAt(i) => null;
         E elementAt(i) => null;
         E singleWhere(f) => null;
@@ skipping 211 matching lines @@
             operator[]=(index, value) { this[index] = value; }
             add(value) { this[length + 1] = value; }
             insert(index, value) {}
             E get first => this[0];
             E get last => this[0];
             E get single => this[0];
             E removeLast() => this[0];
             E removeAt(index) => this[0];
             E elementAt(index) => this[0];
             E singleWhere(f) => this[0];
+            Iterator<E> get iterator => null; 
           }''',
   'JSBool': 'class JSBool extends Interceptor implements bool {}',
   'JSDouble': 'class JSDouble extends JSNumber implements double {}',
   'JSExtendableArray': 'class JSExtendableArray extends JSMutableArray {}',
   'JSFixedArray': 'class JSFixedArray extends JSMutableArray {}',
   'JSFunction':
       'abstract class JSFunction extends Interceptor implements Function {}',
   'JSIndexable': r'''
       abstract class JSIndexable {
         get length;
@@ skipping 78 matching lines @@
 const Map<String, String> DEFAULT_ISOLATE_HELPER_LIBRARY =
     const <String, String>{
   'startRootIsolate': 'void startRootIsolate(entry, args) {}',
   '_currentIsolate': 'var _currentIsolate;',
   '_callInIsolate': 'var _callInIsolate;',
   '_WorkerBase': 'class _WorkerBase {}',
 };
 
 const Map<String, String> DEFAULT_ASYNC_LIBRARY = const <String, String>{
   'DeferredLibrary': 'class DeferredLibrary {}',
-  'Future': 
+  'Future':
       '''
       class Future<T> {
         Future.value([value]);
       }
       ''',
   'Stream': 'class Stream<T> {}',
   'Completer': 'class Completer<T> {}',
   'StreamIterator': 'class StreamIterator<T> {}',
 };
 
@@ skipping 31 matching lines @@
 
     const LookupMap(this._entries, [this._nestedMaps = const []])
         : _key = null, _value = null;
 
     const LookupMap.pair(this._key, this._value)
         : _entries = const [], _nestedMaps = const [];
     V operator[](K k) => null;
   }''',
   '_version': 'const _version = "0.0.1+1";',
 };