This is just a refactoring in preparation for typing the speculative
integer operation as safe integers.

Bug: v8:5267
Change-Id: I56da91a72655a0733b2cf04afcf33cb1d2aa1415
Reviewed-on: https://chromium-review.googlesource.com/637830Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47640}