Support both older and newer implementations of dart:async.

lib/transformations/continuation.dart

 // Copyright (c) 2016, 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 kernel.transformations.continuation;
 
 import 'dart:math' as math;
 
 import '../ast.dart';
 import '../visitor.dart';
@@ skipping 845 matching lines @@
         }
       }
       throw 'Procedure "$name" not found';
     }
 
     var asyncLibrary = findLibrary('dart:async');
     var coreLibrary = findLibrary('dart:core');
 
     var completerClass = findClass(asyncLibrary, 'Completer');
     var futureClass = findClass(asyncLibrary, 'Future');
-    var streamIteratorClass = findClass(asyncLibrary, '_StreamIterator');
+
+    // The VM's dart:async implementation has renamed _StreamIteratorImpl to
+    // _StreamIterator.  To support both old and new library implementations we
+    // look for the old name first and then the new name.
+    var streamIteratorClass;
+    try {
+      streamIteratorClass = findClass(asyncLibrary, '_StreamIteratorImpl');
+    } catch (e) {
+      if (e == 'Class "_StreamIteratorImpl" not found') {
+        streamIteratorClass = findClass(asyncLibrary, '_StreamIterator');
+      } else {
+        rethrow;
+      }
+    }
+
     var syncIterableClass = findClass(coreLibrary, '_SyncIterable');
     var streamControllerClass =
         findClass(asyncLibrary, '_AsyncStarStreamController');
 
     return new HelperNodes(
         asyncLibrary,
         coreLibrary,
         findProcedure(coreLibrary, 'print'),
         findFactoryConstructor(completerClass, 'sync'),
         findConstructor(syncIterableClass, ''),
         findConstructor(streamIteratorClass, ''),
         findFactoryConstructor(futureClass, 'microtask'),
         findConstructor(streamControllerClass, ''),
         findProcedure(asyncLibrary, '_asyncThenWrapperHelper'),
         findProcedure(asyncLibrary, '_asyncErrorWrapperHelper'),
         findProcedure(asyncLibrary, '_awaitHelper'));
   }
 }