Bug 1053999 - Conservative stack check should assume untrusted code, r=bholley

--HG--
extra : rebase_source : f363a8bc1c2f78e9ab47538cdcf8669275a73cb0
Bug 1053999 - Switch chrome stack check to use StackForSystemCode, r=bholley

--HG--
extra : rebase_source : 89fe8ac209cec4e626c6c92fa6cee35c8addc395