Big merge from experimental to bleeding edge.

sdk/lib/_internal/compiler/implementation/js_backend/runtime_types.dart

 // Copyright (c) 2012, 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.
 
 part of js_backend;
 
 /// For each class, stores the possible class subtype tests that could succeed.
 abstract class TypeChecks implements Iterable<ClassElement> {
   /// Get the set of checks required for class [element].
   Iterable<ClassElement> operator[](ClassElement element);
@@ skipping 149 matching lines @@
   Iterable<ClassElement> operator[](ClassElement element) {
     Set<ClassElement> result = map[element];
     return result != null ? result : const <ClassElement>[];
   }
 
   void add(ClassElement cls, ClassElement check) {
     map.putIfAbsent(cls, () => new Set<ClassElement>());
     map[cls].add(check);
   }
 
-  Iterator<ClassElement> iterator() => map.keys.iterator();
+  Iterator<ClassElement> get iterator => map.keys.iterator;
 }