Convert object to fast mode after creation. That enables more optimizations.

Review URL: http://codereview.chromium.org/155405

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2433 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/apinatives.js

@@ -51,6 +51,7 @@ function Instantiate(data, name) {
       var Constructor = %GetTemplateField(data, kApiConstructorOffset);
       var result = Constructor ? new (Instantiate(Constructor))() : {};
       ConfigureTemplateInstance(result, data);
+      result = %ToFastProperties(result);
       return result;
     default:
       throw 'Unknown API tag <' + tag + '>';