Add unhandledExceptionCallback to streamSpawnFunction.

sdk/lib/_internal/compiler/implementation/lib/isolate_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:isolate library.
 
 import 'dart:_isolate_helper' show IsolateNatives,
                                    lazyPort,
                                    ReceivePortImpl;
 
 patch class _Isolate {
   patch static ReceivePort get port {
     if (lazyPort == null) {
       lazyPort = new ReceivePort();
     }
     return lazyPort;
   }
 
   patch static SendPort spawnFunction(void topLevelFunction(),
-      [bool UnhandledExceptionCallback(IsolateUnhandledException e)]) {
-    // TODO(9012): Don't ignore the UnhandledExceptionCallback.
+      [bool unhandledExceptionCallback(IsolateUnhandledException e)]) {
+    if (unhandledExceptionCallback != null) {
+      // TODO(9012): Implement the UnhandledExceptionCallback.
+      throw new UnimplementedError(
+          "spawnFunction with unhandledExceptionCallback");
+    }
     return IsolateNatives.spawnFunction(topLevelFunction);
   }
 
   patch static SendPort spawnUri(String uri) {
     return IsolateNatives.spawn(null, uri, false);
   }
 }
 
 /** Default factory for receive ports. */
 patch class ReceivePort {
   patch factory ReceivePort() {
     return new ReceivePortImpl();
   }
 }