Delete dart2js specific private library code

tool/input_sdk/patch/async_patch.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.
 
 // Patch file for the dart:async library.
 
 import 'dart:_js_helper' show
     patch,
     Primitives,
-    convertDartClosureToJS,
-    requiresPreamble;
+    convertDartClosureToJS;
 import 'dart:_isolate_helper' show
     IsolateNatives,
     TimerImpl,
     leaveJsAsync,
     enterJsAsync,
     isWorker;
 
 import 'dart:_foreign_helper' show JS;
 
 @patch
 class _AsyncRun {
   @patch
   static void _scheduleImmediate(void callback()) {
     scheduleImmediateClosure(callback);
   }
 
   // Lazily initialized.
   static final Function scheduleImmediateClosure =
       _initializeScheduleImmediate();
 
   static Function _initializeScheduleImmediate() {
-    requiresPreamble();
     if (JS('', 'self.scheduleImmediate') != null) {
       return _scheduleImmediateJsOverride;
     }
     if (JS('', 'self.MutationObserver') != null &&
         JS('', 'self.document') != null) {
       // Use mutationObservers.
       var div = JS('', 'self.document.createElement("div")');
       var span = JS('', 'self.document.createElement("span")');
       var storedCallback;
 
@@ skipping 72 matching lines @@
   @patch
   static Timer _createPeriodicTimer(Duration duration,
                              void callback(Timer timer)) {
     int milliseconds = duration.inMilliseconds;
     if (milliseconds < 0) milliseconds = 0;
     return new TimerImpl.periodic(milliseconds, callback);
   }
 }
 
 bool get _hasDocument => JS('String', 'typeof document') == 'object';