Let parser handle factory modifiers.

pkg/compiler/lib/src/parser/node_listener.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.
 
 library dart2js.parser.node_listener;
 
 import '../common.dart';
 import '../elements/elements.dart' show CompilationUnitElement;
 import 'package:front_end/src/fasta/parser/parser.dart'
     show FormalParameterType;
@@ skipping 846 matching lines @@
     pushNode(new EmptyStatement(token));
   }
 
   @override
   void endFactoryMethod(Token beginToken, Token endToken) {
     super.endFactoryMethod(beginToken, endToken);
     Statement body = popNode();
     AsyncModifier asyncModifier = popNode();
     NodeList formals = popNode();
     Node name = popNode();
+    popNode(); // Discard modifiers. They're recomputed below.
 
     // TODO(ahe): Move this parsing to the parser.
     int modifierCount = 0;
     Token modifier = beginToken;
     if (modifier.stringValue == "external") {
       handleModifier(modifier);
       modifierCount++;
       modifier = modifier.next;
     }
     if (modifier.stringValue == "const") {
@@ skipping 134 matching lines @@
     }
     lastErrorWasNativeFunctionBody = false;
   }
 
   void internalError({Token token, Node node}) {
     // TODO(ahe): This should call reporter.internalError.
     Spannable spannable = (token == null) ? node : token;
     throw new SpannableAssertionFailure(spannable, 'Internal error in parser.');
   }
 }