[ComputePressure] Use HasImplicitFocus() for workers.

This CL uses HasImplicitFocus() for workers to support workers in
privacy algos and also makes the change covered by corresponding
browser tests.

Bug: 1425053
Change-Id: If76c1bf7c27d4c776aa463b63546f64b0c5e267d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4976057
Commit-Queue: Wei4 Wang <wei4.wang@intel.com>
Reviewed-by: Raphael Kubo Da Costa <raphael.kubo.da.costa@intel.com>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1237402}