[ios] Apply ios time ticks fixes to partition alloc base

In crrev.com/c/4225015, some code in time_mac.mm was updated. This
patch simply applies anthonyvd@'s work to partition alloc's copy of
base.

Bug: None
Change-Id: I4d03851da1998eec6e34118598b3481a4dd681a1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4236935


Reviewed-by: Anthony Vallée-Dubois <anthonyvd@chromium.org>
Commit-Queue: Ian Vollick <vollick@chromium.org>
Reviewed-by: Francois Pierre Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1103457}