Re-apply 'Unify dart:isolate.' with fixes for autogenerated dart2js and dartium html files.

lib/js_isolate_impl/isolate.dart

Index: lib/js_isolate_impl/isolate.dart
diff --git a/lib/isolate/serialization.dart b/lib/js_isolate_impl/isolate.dart
similarity index 96%
rename from lib/isolate/serialization.dart
rename to lib/js_isolate_impl/isolate.dart
index cd90d92405c4a3ef1d4cfc26cb8756efbc47007f..8d9413cc64b33bcdeb757200cf460d4228a5fa50 100644
--- a/lib/isolate/serialization.dart
+++ b/lib/js_isolate_impl/isolate.dart
@@ -2,6 +2,12 @@
 // 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.
+
+/********************************************************
+  Inserted from lib/isolate/serialization.dart
+ ********************************************************/
+
 class _MessageTraverserVisitedMap {
 
   operator[](var object) => null;
@@ -204,3 +210,4 @@ class _Deserializer {
     throw "Unexpected serialized object";
   }
 }
+