Fix error in CheckedNumeric usage comment
Fix error in CheckedNumeric usage comment

TBR=brucedawson@chromium.org
R=brucedawson@chromium.org

Review URL: https://codereview.chromium.org/1560253002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#367699}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk