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

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

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20375 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Only assign environments when they are actually needed. (ARM and ARM64 only)

Twin of https://codereview.chromium.org/210783003/ and https://codereview.chromium.org/211153003/.

Cleaned up DoChange a bit on the way, making things more uniform across platforms, removed useless comments etc.

R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/214613004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20376 ce2b1a6d-e550-0410-aec6-3dcde31c8c00