Fixing clang-tidy warning.
Replace 0 with nullptr.
Add NOLINT for special cases.
Add default/override to methods.

Bug: v8:8015
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: Iff483356ace471d816051c6dd06ca08809ae1c09
Reviewed-on: https://chromium-review.googlesource.com/1238333Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Florian Sattler <sattlerf@google.com>
Cr-Commit-Position: refs/heads/master@{#56129}