[base] Add current process type / name

Allow the code to get a type of a current process to allow splitting
low-level metrics like number of tasks/IPCs on that dimension.

Restrict access to an explicit allow-list to prevent layering
violations/behavioural differences depending on the current process type.

Bug: b/242853904
Change-Id: I21722ca2d1452e2446348697cfa51972913808d4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3987564
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Aman Verma <amanvr@google.com>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1068537}