Port ad3546ab

Original Commit Message:

    This is an initial step towards clarifying the layout of the
    instruction area. As follow-ups, we should remove additional
    safepoint and handler table offset parameters, and perhaps alter
    Code::safepoint_table_offset (handler_table) semantics to always
    contain a real offset and avoid the magic 0 signifying nonexistent
    tables.

R=jgruber@chromium.org, joransiu@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=
LOG=N

Change-Id: I6c2d3244710f8f3f33bcceb3988e19547f55fba0
Reviewed-on: https://chromium-review.googlesource.com/c/1446138Reviewed-by: Milad Farazmand <miladfar@ca.ibm.com>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#59218}