Cleanups needed for async step-out

runtime/lib/async_patch.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.
 
 import "dart:_internal" hide Symbol;
 
 // Equivalent of calling FATAL from C++ code.
 _fatal(msg) native "DartAsync_fatal";
 
 // We need to pass the value as first argument and leave the second and third
@@ skipping 224 matching lines @@
 @patch
 class _StreamImpl<T> {
   /// The closure implementing the async[*]-body that is `await`ing this future.
   Function _awaiter;
 
   /// The closure implementing the async-generator body that is creating events
   /// for this stream.
   Function _generator;
 }
 
+void _completeOnAsyncReturn(Object completer, [value]) {

[rmacnak, 2017/03/27 21:05:51]

You always call this with both arguments, so don't make [value] optional.

[Cutch, 2017/03/27 22:31:20]

Done.

+  completer.complete(value);
+}
+
 /// Returns a [StackTrace] object containing the synchronous prefix for this
 /// asynchronous method.
 Object _asyncStackTraceHelper(Function async_op)
     native "StackTrace_asyncStackTraceHelper";
 
 void _clearAsyncThreadStackTrace()
     native "StackTrace_clearAsyncThreadStackTrace";
 
 void _setAsyncThreadStackTrace(StackTrace stackTrace)
     native "StackTrace_setAsyncThreadStackTrace";
 
 void _moveNextDebuggerStepCheck(Function async_op)
     native "AsyncStarMoveNext_debuggerStepCheck";