PPC: Reland "Merge old data and pointer space."
PPC: Reland "Merge old data and pointer space."

Port 59be4ba7f4f70dedcaac60914adaa2885a3da5d0

Original commit message:
This reverts commit cbfcee557503514bef20abdfc78ceb262c9c4d64.

R=mbrandy@us.ibm.com

BUG=

Review URL: https://codereview.chromium.org/1074953002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#27723}

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh