js/core: vom compatibilty test, check decoded type toString
js/core: vom compatibilty test, check decoded type toString

We check the decoded type's toString to be extra certain that
it is of the correct type post-decode.

https://github.com/veyron/release-issues/issues/1191

Change-Id: Idd5585a522c038111253fd5e1ec36c40af51d62a

vanadium/js,vanadium/js,vanadium/js,vanadium/js