For instance, it now knows that Number(x) has type Number.

(In this particular case, we used to know that already due to
js-call-reduction of Number but that was recently disabled because
of BigInts.)

Bug: v8:6791
Change-Id: If5c57d46fc8448ca530a9ce7c9d14d63daa0f31c
Reviewed-on: https://chromium-review.googlesource.com/811264Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49909}