isolates refactor: this change introduces 'dart:isolate' as a library. This is a

compiler/lib/implementation/isolate.js

Index: compiler/lib/implementation/isolate.js
diff --git a/compiler/lib/implementation/isolate.js b/compiler/lib/implementation/isolate.js
index ce79d67f778127cd715d0d4519d29576983cc85e..80b3dd327428b82b4b946f953bdd7479536474e8 100644
--- a/compiler/lib/implementation/isolate.js
+++ b/compiler/lib/implementation/isolate.js
@@ -2,6 +2,9 @@
 // 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.
 
+// TODO(sigmund): this file should be removed when the dart code generation
+// backend is deleted.
+
 var isolate$current = null;
 var isolate$rootIsolate = null;  // Will only be set in the main worker.
 var isolate$inits = [];