This reverts commit f2cd10db.

Reason for revert: Blocks the roll https://chromium-review.googlesource.com/c/chromium/src/+/674623

Original change's description:
> Reland "[Memory] Move VirtualMemory out of base:: platform."
> 
> This is a reland of 4dd293d9
> Original change's description:
> > [Memory] Move VirtualMemory out of base:: platform.
> > 
> > - Moves base::VirtualMemory to v8::internal::VirtualMemory.
> > - Makes VirtualMemory platform-independent by moving internals to new
> >   OS:: static methods, for each platform.
> > 
> > This will make it easier to delegate memory management in VirtualMemory
> > to V8::Platform, so that embedders like Blink can override it. We can't
> > depend on V8::Platform in base/platform.
> > 
> > Bug: chromium:756050
> > Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
> > Change-Id: Iadfe230b6850bd917727a373f277afded9883adf
> > Reviewed-on: https://chromium-review.googlesource.com/653214
> > Commit-Queue: Bill Budge <bbudge@chromium.org>
> > Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#48048}
> 
> Bug: chromium:756050
> Change-Id: Ib492c7c69f1833be127a571808301e96b84b8aa2
> Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
> Reviewed-on: https://chromium-review.googlesource.com/671125
> Commit-Queue: Bill Budge <bbudge@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#48084}

TBR=bbudge@chromium.org,ulan@chromium.org,hpayer@chromium.org,mlippautz@chromium.org,scottmg@chromium.org

Change-Id: I04176d77ca9ad8315b0e1bb2b21f40f2c8ab9536
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:756050
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/674843Reviewed-by: Michael Hablich <hablich@chromium.org>
Commit-Queue: Michael Hablich <hablich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48088}