AllocationSite objects survive if a page moves within new space. The
intended behavior was to update the count only when they are visited by
the Scavenger the first time, as they would die afterwards.

This fixes that case where we would move a page within new space where
most objects survive. We would unnecessarily update the AllocationSite
in this case.

Bug: chromium:651354
Change-Id: Ife4dd3e7f60320e0050e7c83dfc5457f66e2287c
Reviewed-on: https://chromium-review.googlesource.com/541302Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46052}