To distinguish it from PBuffer class in future.

Bug: angleproject:2634
Change-Id: I1e256a74584fb001158465cd3068925847231984
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2281795
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>