fixes #221, initial sync*, async, async* implementation

tool/sdk_expected_errors.txt

Index: tool/sdk_expected_errors.txt
diff --git a/tool/sdk_expected_errors.txt b/tool/sdk_expected_errors.txt
index 337800890ccb1419fec5ba4a82b0a46fd9f62082..75d0a02e15b1b454995a9451ad4f63d78f5e43c8 100644
--- a/tool/sdk_expected_errors.txt
+++ b/tool/sdk_expected_errors.txt
@@ -222,8 +222,8 @@ warning: [DownCastImplicit] length == null ? _create2(buffer, offsetInBytes) : _
 warning: [DownCastComposite] IsolateNatives.spawnFunction(entryPoint, message, paused).then((msg) => new Isolate(msg[1], pauseCapability: msg[2], terminateCapability: msg[3])) (Future<dynamic>) will need runtime check to cast to type Future<Isolate> (dart:isolate, line 168, col 14)
 warning: [DownCastComposite] IsolateNatives.spawnUri(uri, args, message, paused).then((msg) => new Isolate(msg[1], pauseCapability: msg[2], terminateCapability: msg[3])) (Future<dynamic>) will need runtime check to cast to type Future<Isolate> (dart:isolate, line 234, col 14)
 warning: [DownCastComposite] doneHandlers (dynamic) will need runtime check to cast to type Iterable<SendPort> (dart:_isolate_helper, line 574, col 29)
-warning: [DownCastComposite] args (dynamic) will need runtime check to cast to type List<String> (dart:_isolate_helper, line 833, col 37)
-warning: [DownCastComposite] msg['args'] (dynamic) will need runtime check to cast to type List<String> (dart:_isolate_helper, line 880, col 11)
+warning: [DownCastComposite] args (dynamic) will need runtime check to cast to type List<String> (dart:_isolate_helper, line 835, col 37)
+warning: [DownCastComposite] msg['args'] (dynamic) will need runtime check to cast to type List<String> (dart:_isolate_helper, line 882, col 11)
 warning: [DownCastImplicit] indexable (JSIndexable) will need runtime check to cast to type JSArray<dynamic> (dart:_isolate_helper/isolate_serialization.dart, line 89, col 38)
 warning: [DownCastImplicit] serializeTearOff (Function) will need runtime check to cast to type (dynamic) → dynamic (dart:_isolate_helper/isolate_serialization.dart, line 120, col 24)
 warning: [DownCastImplicit] serializeTearOff (Function) will need runtime check to cast to type (dynamic) → dynamic (dart:_isolate_helper/isolate_serialization.dart, line 121, col 26)
@@ -303,10 +303,10 @@ warning: [DownCastComposite] Zone.current.registerUnaryCallback(onListenHandler)
 warning: [DownCastComposite] Zone.current.registerUnaryCallback(onCancelHandler) ((dynamic) → dynamic) will need runtime check to cast to type (StreamSubscription<dynamic>) → void (dart:async/stream_impl.dart, line 814, col 28)
 warning: [DownCastComposite] _futureOrPrefetch (dynamic) will need runtime check to cast to type Future<bool> (dart:async/stream_impl.dart, line 1000, col 14)
 warning: [DownCastComposite] _futureOrPrefetch (dynamic) will need runtime check to cast to type T (dart:async/stream_impl.dart, line 1006, col 22)
-warning: [DownCastComposite] _futureOrPrefetch (dynamic) will need runtime check to cast to type _Future<bool> (dart:async/stream_impl.dart, line 1033, col 31)
-warning: [DownCastComposite] _futureOrPrefetch (dynamic) will need runtime check to cast to type _Future<bool> (dart:async/stream_impl.dart, line 1045, col 31)
-warning: [DownCastComposite] _futureOrPrefetch (dynamic) will need runtime check to cast to type _Future<bool> (dart:async/stream_impl.dart, line 1059, col 31)
-warning: [DownCastComposite] _futureOrPrefetch (dynamic) will need runtime check to cast to type _Future<bool> (dart:async/stream_impl.dart, line 1073, col 31)
+warning: [DownCastComposite] _futureOrPrefetch (dynamic) will need runtime check to cast to type _Future<bool> (dart:async/stream_impl.dart, line 1035, col 31)
+warning: [DownCastComposite] _futureOrPrefetch (dynamic) will need runtime check to cast to type _Future<bool> (dart:async/stream_impl.dart, line 1047, col 31)
+warning: [DownCastComposite] _futureOrPrefetch (dynamic) will need runtime check to cast to type _Future<bool> (dart:async/stream_impl.dart, line 1061, col 31)
+warning: [DownCastComposite] _futureOrPrefetch (dynamic) will need runtime check to cast to type _Future<bool> (dart:async/stream_impl.dart, line 1075, col 31)
 warning: [DownCastComposite] outputData (dynamic) will need runtime check to cast to type T (dart:async/stream_pipe.dart, line 104, col 15)
 warning: [DownCastComposite] _transform(inputEvent) (dynamic) will need runtime check to cast to type T (dart:async/stream_pipe.dart, line 235, col 21)
 warning: [DownCastComposite] _previous (Object) will need runtime check to cast to type T (dart:async/stream_pipe.dart, line 426, col 29)