PartitionAlloc: Improve compatibility with Skia.

Resolve a couple a extra warning displayed when using PartitionAlloc in
Skia. This is due to Skia enabling additional warning and also some
differences due to GCC.

Bug: 351867706
Change-Id: Ide6163643cca391f852118fcb5686d14f0555e52
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7545061
Auto-Submit: Arthur Sonzogni <arthursonzogni@chromium.org>
Reviewed-by: Keishi Hattori <keishi@chromium.org>
Commit-Queue: Keishi Hattori <keishi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1581537}
NOKEYCHECK=True
GitOrigin-RevId: bc65cd2fd75a7117708efefde3d278602d6a77a0