This decouples the checking of the {kJavaScriptCallCodeStartRegister}
from the deoptimization checks. We now rely more heavily on the above
register and should check its validity more broadly. Note that there
also is a bug fix for the ARM port contained in this change.

R=mvstanton@chromium.org

Change-Id: I27d8b72cb2b36a85dae4bbbf35e4dbcf150eac01
Reviewed-on: https://chromium-review.googlesource.com/916242
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51270}