A recorded old-to-old slot may be overwritten with a pointer to a new
space object. If the object containing the slot is trimmed later on,
then the mark-compactor may crash on a stale pointer to new space.

This patch ensures that:
1) On trimming of an object we add it to the invalidated_slots sets.
2) The InvalidatedSlotsFilter::IsValid returns false for slots outside
   the invalidated object unless the page was already swept.

Array left-trimming is handled as a special case because object start
moves and cannot be added to the invalidated set. Instead, we clear
the freed memory so that the recorded slots contain Smi values.

Bug: chromium:870226,chromium:816426
Change-Id: Iffc05a58fcf52ece45fdb085b5d1fd4b3acb5d53
Reviewed-on: https://chromium-review.googlesource.com/1163784
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54953}