Update dart:async to match the Dart repo.

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;
 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);
+    _scheduleImmediateClosure(callback);
   }
 
   // Lazily initialized.
-  static final Function scheduleImmediateClosure =
+  static final Function _scheduleImmediateClosure =
       _initializeScheduleImmediate();
 
   static Function _initializeScheduleImmediate() {
+    // TODO(rnystrom): Not needed by dev_compiler.
+    // 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 68 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';
+@patch
+void _rethrow(Object error, StackTrace stackTrace) {
+  // TODO(rnystrom): Not needed by dev_compiler.
+  // error = wrapException(error);
+  JS("void", "#.stack = #", error, stackTrace.toString());
+  JS("void", "throw #", error);
+}