Optimize dartium dart:html bindings so real world application performance is acceptable. Improves d…

tools/dom/templates/html/impl/impl_MessageEvent.darttemplate

Index: tools/dom/templates/html/impl/impl_MessageEvent.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_MessageEvent.darttemplate b/tools/dom/templates/html/impl/impl_MessageEvent.darttemplate
index 19d77d18d30019b0d7f6700e1a1cd5a3f9e0f33e..1b13a76785dc1b6654fa2b62272cfc419464f4cb 100644
--- a/tools/dom/templates/html/impl/impl_MessageEvent.darttemplate
+++ b/tools/dom/templates/html/impl/impl_MessageEvent.darttemplate
@@ -35,7 +35,7 @@ $if DARTIUM
   @DomName('MessageEvent.data')
   @DocsEditable()
   dynamic get data => convertNativeToDart_SerializedScriptValue(
-      _blink.BlinkMessageEvent.instance.data_Getter_(unwrap_jso(this)));
+      _blink.BlinkMessageEvent.instance.data_Getter_(this));
 
 $else
   // TODO(alanknight): This really should be generated by the