More minor type improvements in dart:async.

sdk/lib/async/async_error.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.
 
 part of dart.async;
 
 _invokeErrorHandler(
     Function errorHandler, Object error, StackTrace stackTrace) {
   if (errorHandler is ZoneBinaryCallback) {
     return errorHandler(error, stackTrace);
   } else {
     ZoneUnaryCallback unaryErrorHandler = errorHandler;
     return unaryErrorHandler(error);
   }
 }
 
 Function _registerErrorHandler<R>(Function errorHandler, Zone zone) {
   if (errorHandler is ZoneBinaryCallback) {
-    return zone.registerBinaryCallback<R, dynamic, StackTrace>(
-        errorHandler as dynamic/*=ZoneBinaryCallback<R, dynamic, StackTrace>*/);
+    return zone.registerBinaryCallback<R, Object, StackTrace>(
+        errorHandler as dynamic/*=ZoneBinaryCallback<R, Object, StackTrace>*/);
   } else {
-    return zone.registerUnaryCallback<R, dynamic>(
-        errorHandler as dynamic/*=ZoneUnaryCallback<R, dynamic>*/);
+    return zone.registerUnaryCallback<R, Object>(
+        errorHandler as dynamic/*=ZoneUnaryCallback<R, Object>*/);
   }
 }
-
-class _UncaughtAsyncError extends AsyncError {
-  _UncaughtAsyncError(error, StackTrace stackTrace)
-      : super(error, _getBestStackTrace(error, stackTrace));
-
-  static StackTrace _getBestStackTrace(error, StackTrace stackTrace) {
-    if (stackTrace != null) return stackTrace;
-    if (error is Error) {
-      return error.stackTrace;
-    }
-    return null;
-  }
-
-  String toString() {
-    String result = "Uncaught Error: ${error}";
-
-    if (stackTrace != null) {
-      result += "\nStack Trace:\n$stackTrace";
-    }
-    return result;
-  }
-}