This reverts commit b35a0789.

Reason for revert: Roll blocker for https://chromium-review.googlesource.com/c/607193

Original change's description:
> [heap, runtime] Fix conversion of large strings to thin strings.
> 
> This patch removes creation of fillers in the middle of a large page and
> fixes assert in Heap::NotifyObjectLayoutChange.
> 
> The fillers in large pages are useless since we do not sweep large
> object space.
> 
> Bug: chromium:752426
> Change-Id: I01c230223f28d6d54b7362ee70e9d83de50678fd
> Reviewed-on: https://chromium-review.googlesource.com/601994
> Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
> Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#47221}

TBR=ulan@chromium.org,jkummerow@chromium.org,mlippautz@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: chromium:752426
Change-Id: I58a632af37fa018d82693099a7a395ca5db5af0f
Reviewed-on: https://chromium-review.googlesource.com/609404Reviewed-by: Michael Hablich <hablich@chromium.org>
Commit-Queue: Michael Hablich <hablich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47262}