Sprinkle some types on the SDK like the static typing fairy.

pkg/dev_compiler/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;
 
+typedef void _Callback();
+typedef void _TakeCallback(_Callback callback);
+
 @patch
 class _AsyncRun {
   @patch
   static void _scheduleImmediate(void callback()) {
     _scheduleImmediateClosure(callback);
   }
 
   // Lazily initialized.
-  static final Function _scheduleImmediateClosure =
+  static final _TakeCallback _scheduleImmediateClosure =
       _initializeScheduleImmediate();
 
-  static Function _initializeScheduleImmediate() {
+  static _TakeCallback _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;
+      _Callback storedCallback;
 
       internalCallback(_) {
         leaveJsAsync();
         var f = storedCallback;
         storedCallback = null;
         f();
       };
 
       var observer = JS('', 'new self.MutationObserver(#)', internalCallback);
       JS('', '#.observe(#, { childList: true })',
@@ skipping 66 matching lines @@
   }
 }
 
 @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);
 }