This hack is causing false "last-resort" garbage collections.

When incremental marking is in progress and overshoots the limit,
our heuristics in the allocator request finishing the mark-compact
because V8 is in optimize-for-memory mode.

However, the mark-compact gets replaced by scavenger which leads to
retrying the allocation two times and eventually doing last resort GC
(which throws away all the marking info).

BUG=chromium:697119

Review-Url: https://codereview.chromium.org/2723003003
Cr-Commit-Position: refs/heads/master@{#43554}