- Moves GetRandomMmapAddr from platform to v8::internal allocation
  primitives, in preparation for delegating this to the embedder.
- Adds hint parameters to OS functions that used to use this function.

Bug: chromium:756050
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: Iad72e6eac9c08a3e22c2cd2b2905623b8e514ae0
Reviewed-on: https://chromium-review.googlesource.com/677777Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48124}