Version 4.3.61.6 (cherry-pick)

Merged 1e022278
Merged 780f33c0

More robust when allocation fails during compaction

Relax heap size assert during compaction

BUG=chromium:473307
LOG=N
R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/1058613003

Cr-Commit-Position: refs/branch-heads/4.3@{#8}
Cr-Branched-From: f5c0a23a-refs/heads/4.3.61@{#1}
Cr-Branched-From: 0a7d4f49-refs/heads/master@{#27508}