Currently Page::ShrinkToHighWaterMark checks that there is only one
filler in the to-be-freed area at the end of the page. This does not
hold if an allocation observer is active.

We should instead check that the to-be-freed area does not contain
allocated objects and will not contain allocated objects:
1) Following chain of fillers we arrive at the end of the page.
2) The free list of the page is empty.

This patch also changes PagedSpace::ResetFreeList to evict free list
entries of each page, instead of just reseting the global free list.

It also removes invalidation of free list categories.
Now FreeList::EvictFreeListItems simply evicts free list entries without
invalidating free list categories.

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I6051578ec2c91c9614d14c7a6ce188d2db5ace3b
Reviewed-on: https://chromium-review.googlesource.com/822571
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50040}