Move template instance check from Object to FunctionTemplateInfo::IsTemplateFor

BUG=
R=dcarney@chromium.org

Review URL: https://chromiumcodereview.appspot.com/67613005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17876 ce2b1a6d-e550-0410-aec6-3dcde31c8c00