Revert "[ArrayBuffer] Give each SecurityOrigin a Partition for ArrayBuffers."

This reverts commit eaa730ff5abd585b0b629f07406df6701589e7ff.

Reason for revert: performance regression:
https://bugs.chromium.org/p/chromium/issues/detail?id=809546

Original change's description:
> [ArrayBuffer] Give each SecurityOrigin a Partition for ArrayBuffers.
> 
> - Goes through SecurityOrigin's ArrayBuffer Partition for ArrayBuffers
>   allocated from the V8 side.
> - Reworks ArrayBufferContents to support multiple partitions for
>   ArrayBuffers. Adds overload of AllocateMemoryOrNull to handle these
>   allocations. Associates a PartitionRootGeneric with each allocation,
>   storing a pointer just before the ArrayBuffer data.
> 
> Bug:chromium:799573
> 
> Change-Id: I712176c715d1fb2511d87892052ba9d2d8084336
> Reviewed-on: https://chromium-review.googlesource.com/853120
> Reviewed-by: Chris Palmer <palmer@chromium.org>
> Reviewed-by: Kentaro Hara <haraken@chromium.org>
> Commit-Queue: Bill Budge <bbudge@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#533921}

TBR=palmer@chromium.org,bbudge@chromium.org,nasko@chromium.org,adamk@chromium.org,haraken@chromium.org,mlippautz@chromium.org

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

Bug: chromium:799573
Change-Id: Id48e51e7d0c53bcb9df15ab72d8ea99014c82055
Reviewed-on: https://chromium-review.googlesource.com/912108
Reviewed-by: Bill Budge <bbudge@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#535966}
3 files changed