- Use overflow-proof HasRemainingBytes
- Add DCHECK to catch index_ OOB in RemainingBytes

Change-Id: I65c47c42438c93c9b4673f09fed4b8ef4685f257
Reviewed-on: https://chromium-review.googlesource.com/c/1388535Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58441}