const constructors with optional arguments.

frog/leg/resolver.dart

 // Copyright (c) 2012, 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.
 
 interface TreeElements {
   Element operator[](Node node);
   Selector getSelector(Send send);
 }
 
 class TreeElementMapping implements TreeElements {
@@ skipping 787 matching lines @@
     TypeAnnotation node = argument.asTypeAnnotation();
     if (node == null) {
       node = argument.asSend().receiver;
     }
     resolveTypeRequired(node);
   }
 
   void handleArguments(Send node) {
     int count = 0;
     List<SourceString> namedArguments = <SourceString>[];
+    bool seenNamedArgument = false;
     for (Link<Node> link = node.argumentsNode.nodes;
          !link.isEmpty();
          link = link.tail) {
       count++;
       Expression argument = link.head;
       visit(argument);
       if (argument.asNamedArgument() != null) {
+        seenNamedArgument = true;
         NamedArgument named = argument;
         namedArguments.add(named.name.source);
+      } else if (seenNamedArgument) {
+        error(argument, MessageKind.INVALID_ARGUMENT_AFTER_NAMED);
       }
     }
     mapping.setSelector(node, new Invocation(count, namedArguments));
   }
 
   visitSend(Send node) {
     Element target = resolveSend(node);
     if (node.isOperator) {
       Operator op = node.selector.asOperator();
       if (op.source.stringValue === 'is') {
@@ skipping 829 matching lines @@
 class TopScope extends Scope {
   LibraryElement get library() => element;
 
   TopScope(LibraryElement library) : super(null, library);
   Element lookup(SourceString name) => library.find(name);
 
   Element add(Element element) {
     throw "Cannot add an element in the top scope";
   }
 }