Replace DCHECK with NOTREACHED

If we somehow end up in PopAndRestore with a stack of size 1, we want to crash in release builds instead of messing with the state stack.

Bug: 1232705
Change-Id: Ie6e7dd674779a400280f59508c00d6fad93f3365
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3070907


Reviewed-by: Juanmi Huertas <juanmihd@chromium.org>
Commit-Queue: Alisa Lin <alisalin@google.com>
Cr-Commit-Position: refs/heads/master@{#908694}