For kUpdateEntry and kRemoveEntry, the ArrayBuffer is no longer present
on the current page. These are the two most common cases; kKeepEntry is
only used for aborted old-page evacuation candidates. Currently we pay
the cost of removing the entry from the array_buffers_ map, even though
the page itself will be cleared (for new space) or only aborted
evacuation candidates will be kept on the page (for old space).

Change-Id: Ib442109d444973a72e378d9072206f404d1c5183
Reviewed-on: https://chromium-review.googlesource.com/1102332Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53757}