Fix chromium-style warning after https://codereview.chromium.org/1639623003/

Also fix a -Wsign-compare warning.

BUG=426656,82385
TBR=robliao@chromium.org

Review URL: https://codereview.chromium.org/1679743004 .

Cr-Commit-Position: refs/heads/master@{#374370}
1 file changed