Port fdb067dc

Original Commit Message:

    This CL introduces those codegen changes necessary for JIT-ing using
    the WasmCodeManager.

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

Change-Id: Iee9f4f63fe28ab2d25b4b37d10e44a7a1337c7e0
Reviewed-on: https://chromium-review.googlesource.com/783877
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Reviewed-by: Mircea Trofin <mtrofin@chromium.org>
Reviewed-by: Joran Siu <joransiu@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#49590}