This is used for internal security checks in eval(). Expose this to
enable the embedder to implement similar security checks.

R=yangguo@chromium.org
BUG=

Change-Id: I10819713b19527622de5ffffac313d126a887c05
Reviewed-on: https://chromium-review.googlesource.com/446106Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43405}