spanification: Add `#pragma allow_unsafe_buffers` to renderer/platform/

https://chromium.googlesource.com/chromium/src/+/main/docs/unsafe_buffers.md#suppressions

This is a preparation to fix each files.
This CL has no behavior changes.

Bug: 351564777
Change-Id: Id7796f9eee104acfa4260a3968ddf05c50408efa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5686213
Reviewed-by: danakj <danakj@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1325158}
NOKEYCHECK=True
GitOrigin-RevId: bde3d0d4b13aee737848caba9b62c37adbbe5806
1 file changed