Make JS runtime only used in the creator thread.\
Because the SpiderMonkey use thread-local storage.\
See https://github.com/ricardoquesada/Spidermonkey/blob/master/mfbt/ThreadLocal.h\
and https://github.com/ricardoquesada/Spidermonkey/blob/abb95806397d0a3523263a1faf5b21923b35f508/js/src/vm/Runtime.cpp