This makes it more clear that we only store i32 values as constants in
the cache state.

R=ahaas@chromium.org

Bug: v8:6600
Change-Id: I3022e963e864c9c533cbb673bd8502481389799b
Reviewed-on: https://chromium-review.googlesource.com/853870Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50437}