8198313: Wrap holder object for ClassLoaderData in a WeakHandle
Summary: Use WeakHandle for ClassLoaderData::_holder so that is_alive closure is not needed
Reviewed-by: rehn, kbarrett
8201321: NMT: Unnecessary re-recording thread stack and size when attaching listener to JavaThread
Summary: Replaced recoding thread stack and size with assertion
Reviewed-by: dholmes, coleenp