update comment to add tracking bug from r1833
update comment to add tracking bug from r1833

TBR=thakis@chromium.org

Review URL: https://codereview.chromium.org/131063004
old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google