cleanup patch generation to preseve comments and remove @patch

test/generated_sdk/lib/async/schedule_microtask.dart

 // Copyright (c) 2013, 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 dart.async;
 
 typedef void _AsyncCallback();
 
 class _AsyncCallbackEntry {
   final _AsyncCallback callback;
@@ skipping 117 matching lines @@
     // No need to bind the callback. We know that the root's scheduleMicrotask
     // will be invoked in the root zone.
     _rootScheduleMicrotask(null, null, _ROOT_ZONE, callback);
     return;
   }
   Zone.current.scheduleMicrotask(
       Zone.current.bindCallback(callback, runGuarded: true));
 }
 
 class _AsyncRun {
-  @patch
+  /** Schedule the given callback before any other event in the event-loop. */
   static void _scheduleImmediate(void callback()) {
     scheduleImmediateClosure(callback);
   }
 }