Reenable support for native factory constructors.

pkg/compiler/lib/src/native/enqueue.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 native;
 
 /**
  * This could be an abstract class but we use it as a stub for the dart_backend.
  */
 class NativeEnqueuer {
@@ skipping 330 matching lines @@
     compiler.backend.registerInstantiatedType(
         classElement.rawType, world, compiler.globalDependencies);
 
     if (firstTime) {
       queue.add(onFirstNativeClass);
     }
   }
 
   registerElement(Element element) {
     reporter.withCurrentElement(element, () {
-      if (element.isFunction || element.isGetter || element.isSetter) {
+      if (element.isFunction ||
+          element.isFactoryConstructor ||
+          element.isGetter ||
+          element.isSetter) {
         handleMethodAnnotations(element);
         if (element.isNative) {
           registerMethodUsed(element);
         }
       } else if (element.isField) {
         handleFieldAnnotations(element);
         if (element.isNative) {
           registerFieldLoad(element);
           registerFieldStore(element);
         }
@@ skipping 314 matching lines @@
         superclass,
         () => <ClassElement>[]);
     directSubtypes.add(cls);
   }
 
   void logSummary(log(message)) {
     log('Compiled ${registeredClasses.length} native classes, '
         '${unusedClasses.length} native classes omitted.');
   }
 }