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

frog/leg/compiler.dart

Index: frog/leg/compiler.dart
===================================================================
--- frog/leg/compiler.dart	(revision 5637)
+++ frog/leg/compiler.dart	(working copy)
@@ -180,9 +180,11 @@
 
   void enableIsolateSupport(LibraryElement element) {
     isolateLibrary = element;
-    addToWorkList(element.find(START_ROOT_ISOLATE)); 
+    addToWorkList(element.find(START_ROOT_ISOLATE));
   }
 
+  bool hasIsolateSupport() => isolateLibrary !== null;
+
   void onLibraryLoaded(LibraryElement library, Uri uri) {
     if (uri.toString() == 'dart:isolate') {
       enableIsolateSupport(library);
@@ -219,6 +221,10 @@
         const SourceString('UNINTERCEPTED'), library), this);
     library.define(new ForeignElement(
         const SourceString('JS_HAS_EQUALS'), library), this);
+    library.define(new ForeignElement(
+        const SourceString('JS_CURRENT_ISOLATE'), library), this);
+    library.define(new ForeignElement(
+        const SourceString('JS_CALL_IN_ISOLATE'), library), this);
   }
 
   void runCompiler(Uri uri) {