GitLab

Consistently fail on detached contexts. Previously, a detached context
could allow for a nullptr deref, and a renderer crash.

Consistently return nullptr for navigator.clipboard, and ensure that
a nullptr navigator.clipboard function will terminate immediately in a
consistent manner.

Also, add tests to ensure that regressions don't occur in the future.

Bug: 10285919, 1034023
Change-Id: I67f8a76dc2901e7447049ff99e0b27ea6afeba63
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2057817
Commit-Queue: Darwin Huang <huangdarwin@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#742941}