Revert of Reduce duplicate code in full-codegen across platforms. (patchset #1 id:1 of https://codereview.chromium.org/1255613002/)

Reason for revert:
breaks mips

Original issue's description:
> Reduce duplicate code in full-codegen across platforms.
>
> R=mvstanton@chromium.org
>
> Committed: https://crrev.com/937d4efbf9c399339fdc8e041bec8e80baa7b58f
> Cr-Commit-Position: refs/heads/master@{#29798}

TBR=mvstanton@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/1252513004

Cr-Commit-Position: refs/heads/master@{#29802}