fixes #28032, await in cascade

pkg/dev_compiler/lib/src/compiler/js_metalet.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.
 
 // TODO(jmesserly): import from its own package
 import '../js_ast/js_ast.dart';
 import '../js_ast/precedence.dart';
 
 import 'js_names.dart' show TemporaryId;
 
@@ skipping 315 matching lines @@
   @override
   visitNode(Node node) {
     if (!found) super.visitNode(node);
   }
 }
 
 class _YieldFinder extends BaseVisitor {
   bool hasYield = false;
   bool hasThis = false;
   bool _nestedFunction = false;
+
   @override
   visitThis(This node) {
     hasThis = true;
   }
 
   @override
   visitFunctionExpression(FunctionExpression node) {
     var savedNested = _nestedFunction;
     _nestedFunction = true;
     super.visitFunctionExpression(node);
     _nestedFunction = savedNested;
   }
 
   @override
   visitYield(Yield node) {
     if (!_nestedFunction) hasYield = true;
   }
 
   @override
   visitNode(Node node) {
-    if (!hasYield) super.visitNode(node);

[Jennifer Messerly, 2016/12/07 21:57:20]

DOH!

+    if (hasYield && hasThis) return; // found both, nothing more to do.
+    super.visitNode(node);
   }
 }