[PA] Copy //base/files/platform_file.h to PartitionAllocator's base.

PS1 = baseline

Bug: chromium:40238514
Change-Id: Iefc882063ca7cdb7508ec4ff133b66be524151a4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6097765
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Commit-Queue: Takashi Sakamoto <tasak@google.com>
Cr-Commit-Position: refs/heads/main@{#1399048}
NOKEYCHECK=True
GitOrigin-RevId: 0b1d5c77a73caf7182b9294ca21411fb30ebcc07
5 files changed