For each new major OS version, we need to poke at the internals
of CFAllocator to enable the out-of-memory killer for the default
CFAllocator implementations.

This update is for macOS 10.13 ("High Sierra"), whose CFAllocator
internals are unchanged from 10.12 (and in fact from 10.7). It also
updates the base::mac::IsOS*() family of functions for this new OS
version.

BUG=45650
TEST=base_unittests OutOfMemoryDeathTest.CFAllocator*,MacUtilTest.IsOSEllipsis

Change-Id: I700878b1e0baef658b6d7d618cbeb513386a79eb
Reviewed-on: https://chromium-review.googlesource.com/565467


Reviewed-by: Mark Mentovai <mark@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#485358}