We can improve performance of inlined Array.prototype.map if we statically
know the type of the callback return result is a SignedSmall. Indeed,
we no longer need bother with transitioning the output array, because we
can store a SignedSmall (aka "Smi") anywhere.

Bug: v8:6896
Change-Id: I140ce9a7c15ff77d05afeda6cda58f0560d922c8
Reviewed-on: https://chromium-review.googlesource.com/707139Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48387}