The optimization

  NumberFloor(NumberDivide(lhs, rhs))

to

  NumberToInt32(NumberDivide(lhs, rhs))

for potentially negative lhs is not valid, since Math.floor rounds
towards -infinity, whereas ToInt32 truncates.

BUG=chromium:699282
R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2743673002
Cr-Commit-Position: refs/heads/master@{#43699}