We use CheckNumber to guard values as being proper numbers, i.e. if the
input value is anything but a Number, we deoptimize. This follows the
existing effect/control linearization magic that we already use for the
other checks.

R=jarin@chromium.org
BUG=v8:5141

Review-Url: https://codereview.chromium.org/2109623002
Cr-Commit-Position: refs/heads/master@{#37329}