Support both older and newer implementations of dart:async.

lib/transformations/continuation.dart

Index: lib/transformations/continuation.dart
diff --git a/lib/transformations/continuation.dart b/lib/transformations/continuation.dart
index 821933b03ef6ef68e2b4197a802efbe067201c49..eebd307c7bf69449de5f4f8352e64396f566db17 100644
--- a/lib/transformations/continuation.dart
+++ b/lib/transformations/continuation.dart
@@ -863,7 +863,21 @@ class HelperNodes {
 
     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');