v8binding: Check the "script forbidden" status in IDL callbacks.

Checks whether script execution is allowed or not in IDL callbacks.
See the bug for details.

Bug: 964928
Change-Id: Icfe11d7cd029a52794cdd4525d04288735dc3b29
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1624985
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Hitoshi Yoshida <peria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662548}
18 files changed