Revert "[Memory] Use OS::Allocate for all OS memory allocations."

This reverts commit 7e78506f.

Reason for revert: Breaks roll:
https://build.chromium.org/p/tryserver.chromium.android/builders/android_arm64_dbg_recipe/builds/381619

Original change's description:
> [Memory] Use OS::Allocate for all OS memory allocations.
> 
> - Eliminates OS::ReserveRegion and OS::ReserveAlignedRegion.
> - Changes OS::Allocate to take alignment parameter, reorders parameters
>   to match page_allocator.
> - Since the size of memory allocation can be deduced, don't return the
>   amount of memory allocated.
> - Changes reservation of aligned address space. Before we would reserve
>   (size + alignment) rounded up to page size. This is too much, because
>   maximum misalignment is (alignment - page_size).
> - On Windows and Cygwin, we release an oversize allocation and
>   immediately retry at the aligned address in the allocation. If we
>   lose the address due to a race, we just retry.
> - Clean up all the calls to OS::Allocate in codegen and tests by adding
>   helper AllocateSystemPage function (allocation.h) and
>   AllocateAssemblerBuffer (cctest.h).
> - Changes 'assm' to 'masm' in some targets for consistency when using
>   a macro-assembler.
> 
> Bug: chromium:756050
> Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
> Change-Id: I306dbe042cc867670fdc935abca29db074b0da71
> Reviewed-on: https://chromium-review.googlesource.com/749848
> Commit-Queue: Bill Budge <bbudge@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Reviewed-by: Hannes Payer <hpayer@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#49235}

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

Change-Id: If538a174d048e0416b4374426df721d4ea84cd4c
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/758860Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49249}