dart2js: support tear-offs in the startup emitter.

pkg/compiler/lib/src/patch_parser.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.
 
 /**
  * This library contains the infrastructure to parse and integrate patch files.
  *
  * Three types of elements can be patched: [LibraryElement], [ClassElement],
  * [FunctionElement]. Patches are introduced in patch libraries which are loaded
  * together with the corresponding origin library. Which libraries that are
@@ skipping 422 matching lines @@
   const PatchAnnotationHandler();
 
   PatchVersion getPatchVersion(MetadataAnnotation annotation) {
     if (annotation.beginToken != null) {
       if (annotation.beginToken.next.value == 'patch') {
         return const PatchVersion(null);
       } else if (annotation.beginToken.next.value == 'patch_full') {
         return const PatchVersion('full');
       } else if (annotation.beginToken.next.value == 'patch_lazy') {
         return const PatchVersion('lazy');
+      } else if (annotation.beginToken.next.value == 'patch_startup') {
+        return const PatchVersion('startup');
       }
     }
     return null;
   }
 
   @override
   PatchVersion apply(Compiler compiler,
                      Element element,
                      MetadataAnnotation annotation) {
     return getPatchVersion(annotation);
@@ skipping 115 matching lines @@
 
 class PatchVersion {
   final String tag;
 
   const PatchVersion(this.tag);
 
   bool isActive(String patchTag) => tag == null || tag == patchTag;
 
   String toString() => 'PatchVersion($tag)';
 }