Add support for the new function-type syntax.

pkg/compiler/lib/src/resolution/resolution_common.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.resolution.common;
 
 import '../common.dart';
 import '../common/resolution.dart' show Resolution;
 import '../elements/elements.dart';
 import '../tree/tree.dart';
@@ skipping 38 matching lines @@
   Scope get scope;
 
   MappingVisitor(Resolution resolution, this.registry)
       : typeResolver = new TypeResolver(resolution),
         super(resolution);
 
   AsyncMarker get currentAsyncMarker => AsyncMarker.SYNC;
 
   /// Add [element] to the current scope and check for duplicate definitions.
   void addToScope(Element element) {
+    if (element is FormalElement && element.isUnnamed) {
+      // No duplicate names possible.
+      return;
+    }
     Element existing = scope.add(element);
     if (existing != element) {
       reportDuplicateDefinition(element.name, element, existing);
     }
   }
 
   void checkLocalDefinitionName(Node node, Element element) {
     if (currentAsyncMarker != AsyncMarker.SYNC) {
       if (element.name == 'yield' ||
           element.name == 'async' ||
@@ skipping 19 matching lines @@
       String name, Spannable definition, Spannable existing) {
     reporter.reportError(
         reporter.createMessage(
             definition, MessageKind.DUPLICATE_DEFINITION, {'name': name}),
         <DiagnosticMessage>[
           reporter.createMessage(
               existing, MessageKind.EXISTING_DEFINITION, {'name': name}),
         ]);
   }
 }