Rename MarkCompactCollector::StealMemoryFromSweeperThreads to RefillFreeLists

The swept memory is now collected on the foreground thread, so it's not
stealing the memory from the threads anymore

BUG=v8:3104
R=hpayer@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/143463005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18710 ce2b1a6d-e550-0410-aec6-3dcde31c8c00