Move storeInc() to where USE_LONG_LONG is visible.

Follow-up for r161679.

BUG=315884
R=hans@chromium.org
TBR=cevans

Review URL: https://codereview.chromium.org/67883002

git-svn-id: svn://svn.chromium.org/blink/trunk@161688 bbb929c8-8fbe-4397-9dbb-9b2b20218538