Add support for capturing and changing the current isolate in the closure wrapper.

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 24 matching lines @@
  * [spawnFunction] and [spawnUri], and we have an API to spawn DOM isolates.
  */
 #library("dart:isolate");
 
 #import("dart:uri");
 #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) {
+  isolate.eval(function);
+  _globalState.topEventLoop.run();
+}
+
+/**
+ * Called by the compiler to fetch the current isolate context.
+ */
+void _currentIsolate() => _globalState.currentContext;