Store i18n meta data in hidden symbols instead of js accessible properties

There were some tests that are supposed to protect against js messing
with the meta data, however, they just didn't try hard enough.

BUG=354967
R=dcarney@chromium.org
LOG=y

Committed: https://code.google.com/p/v8/source/detail?r=20375

Review URL: https://codereview.chromium.org/215293005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20388 ce2b1a6d-e550-0410-aec6-3dcde31c8c00