Fixing clang-tidy warning.

Bug: v8:8015
Cq-Include-Trybots: luci.chromium.try:linux_chromium_headless_rel;luci.chromium.try:linux_chromium_rel_ng;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I5404f0b94c7badce2c59d8eac2c32810f4fa2c3c
Reviewed-on: https://chromium-review.googlesource.com/1224317Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Florian Sattler <sattlerf@google.com>
Cr-Commit-Position: refs/heads/master@{#55914}