isolate-leg: fix typo in type signature.

lib/isolate/isolate_leg.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.
 
 
 /**
  * The `dart:isolate` library defines APIs to spawn and communicate with
  * isolates.
  *
  * All code in dart runs in the context of an isolate. Each isolate has its own
@@ skipping 29 matching lines @@
 #source("isolate_api.dart");
 #source("frog/compiler_hooks.dart");
 #source("frog/isolateimpl.dart");
 #source("frog/ports.dart");
 #source("frog/messages.dart");
 
 /**
  * Called by the compiler to support switching
  * between isolates when we get a callback from the DOM.
  */
-void _callInIsolate(IsolateContext isolate, Function function) {
+void _callInIsolate(_IsolateContext isolate, Function function) {
   isolate.eval(function);
   _globalState.topEventLoop.run();
 }
 
 /**
  * Called by the compiler to fetch the current isolate context.
  */
 void _currentIsolate() => _globalState.currentContext;