Affects the Windows case where we over reserve for alignment reasons but
actually already get aligned memory.

Implemented on allocator level to potentially cover other platforms as
well.

Bug: 
Change-Id: I4859451f157e1e363db27413a43345fdd1990a06
Reviewed-on: https://chromium-review.googlesource.com/535454
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45970}