Fix aborting compaction for pages by doing two separate passes, one that scans
all live objects, and one that later on sweeps the page.

Detailed description see bug report.

BUG=chromium:539356,chromium:524425
LOG=N

Review URL: https://codereview.chromium.org/1413763011

Cr-Commit-Position: refs/heads/master@{#31526}