[base] Add Dead Type to base::Value

This change adds a temporary DEAD type to base::Value which should help
to track down use-after-free bugs. Furthermore, this change also removes
the now unneeded is_alive_ flag.

Bug: 859477, 941404
Change-Id: I9b7a2f3cbb0b22d7e3ed35b2453537419f3f7e55
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1478897
Reviewed-by: Pavol Marko <pmarko@chromium.org>
Reviewed-by: Tao Bai <michaelbai@chromium.org>
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Mike Pinkerton <pinkerton@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: David Turner <digit@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641404}
14 files changed