Add support for JS->Dart and Dart->dart via *PortSync.

lib/dom/templates/html/frog/impl_Window.darttemplate

Index: lib/dom/templates/html/frog/impl_Window.darttemplate
diff --git a/lib/dom/templates/html/frog/impl_Window.darttemplate b/lib/dom/templates/html/frog/impl_Window.darttemplate
index 0f076ebf774ac373bde4793b72e68d733c852b9e..77c215c3f3fc6fa51120b6e36ebff4227189a975 100644
--- a/lib/dom/templates/html/frog/impl_Window.darttemplate
+++ b/lib/dom/templates/html/frog/impl_Window.darttemplate
@@ -118,11 +118,16 @@ class $CLASSNAME$EXTENDS$IMPLEMENTS native "@*DOMWindow" {
   _IDBFactoryImpl _get_indexedDB() native
       'return this.indexedDB || this.webkitIndexedDB || this.mozIndexedDB';
 
-  // TODO(kasperl): Document this.
+  // TODO(kasperl): Document these.
   lookupPort(String name) {
     var port = JSON.parse(localStorage['dart-port:$name']);
     return _deserialize(port);
   }
 
+  registerPort(String name, var port) {
+    var serialized = _serialize(port);
+    localStorage['dart-port:$name'] = JSON.stringify(serialized);
+  }
+
 $!MEMBERS
 }