implement null aware ops, fixes #249

test/codegen/language/async_star_test.dart

 // Copyright (c) 2015, 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 async_start_test;
 
 import "package:unittest/unittest.dart";
 import "dart:async";
 
 main() {
@@ skipping 720 matching lines @@
         sub.pause();                                              /// 02: continued
         return sync.wait();                                       /// 02: continued
       }).whenComplete(() {                                        /// 02: continued
         expect(list, equals(["*1", 1, "*2"]));                    /// 02: continued
         sub.cancel();                                             /// 02: continued
         return new Future.delayed(MS * 200, () {                  /// 02: continued
           // Should not have yielded 2 or added *3 while paused.  /// 02: continued
           expect(list, equals(["*1", 1, "*2"]));                  /// 02: continued
         });                                                       /// 02: continued
       });                                                         /// 02: continued
-    }, skip: "other impls aren't passing this test, see "
-        "https://github.com/dart-lang/sdk/issues/22853");                                                           /// 02: continued
+    });                                                           /// 02: continued
   });
 
   group("await for", () {
     mkStream(int n) async* {
       for (int i = 0; i < n; i++) yield i;
     }
 
     test("simple stream", () {
       f(s) async {
         var r = 0;
@@ skipping 111 matching lines @@
       f(s) async {                                                   /// 05: continued
         var r = 0;                                                   /// 05: continued
         await for (var i in s) {                                     /// 05: continued
           r += await new Future.delayed(MS * 10, () => i);           /// 05: continued
         }                                                            /// 05: continued
         return r;                                                    /// 05: continued
       }                                                              /// 05: continued
       return f(sc.stream).then((v) {                                 /// 05: continued
         expect(v, equals(10));                                       /// 05: continued
       });                                                            /// 05: continued
-    }, skip: "other impls aren't passing this test, see "
-        "https://github.com/dart-lang/sdk/issues/22853");                                                              /// 05: continued
+    });                                                              /// 05: continued
   });
 }
 
 // Obscuring identity function.
 id(x) {
   try {
     if (x != null) throw x;
   } catch (e) {
     return e;
   }
@@ skipping 37 matching lines @@
   }
 
   // Release whoever is currently waiting.
   void release([v]) {
     if (_completer != null) {
       _completer.complete(v);
       _completer = null;
     }
   }
 }