Preserve async markers when parsing js_ast

pkg/dev_compiler/lib/src/js_ast/template.dart

 // Copyright (c) 2014, 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.
 
 part of js_ast;
 
 class TemplateManager {
   Map<String, Template> expressionTemplates = new Map<String, Template>();
   Map<String, Template> statementTemplates = new Map<String, Template>();
 
@@ skipping 652 matching lines @@
         if (result is Iterable) {
           for (var r in result) params.add(r);
         } else {
           params.add(result);
         }
       }
       var body = makeBody(arguments);
       if (node is ArrowFun) {
         return new ArrowFun(params, body);
       } else if (node is Fun) {
-        return new Fun(params, body);
+        return new Fun(params, body,
+            isGenerator: node.isGenerator, asyncModifier: node.asyncModifier);
       } else {
         throw "Unknown FunctionExpression type ${node.runtimeType}: $node";
       }
     };
   }
 
   Instantiator visitFun(Fun node) => visitFunctionExpression(node);
 
   Instantiator visitArrowFun(ArrowFun node) => visitFunctionExpression(node);
 
@@ skipping 228 matching lines @@
     if (count != before) containsInterpolatedNode.add(node);
     return null;
   }
 
   visitInterpolatedNode(InterpolatedNode node) {
     containsInterpolatedNode.add(node);
     if (node.isNamed) holeNames.add(node.nameOrPosition);
     ++count;
   }
 }