Update PlusAddressService creation function signature

This CL passes origin by ref and updates documentation. It also removes
the virtual keyword now that the service need not be mocked. This
function is likely to be removed in the future, deferring instead to UI
orchestration, which will have options to fill immediately or trigger a
modal. There is no intended functional change with this CL.

Change-Id: Id6baa08301bfbe132bc37dc97b1ef5aa2c7999fe
Bug: 1467623
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4808902


Reviewed-by: Kirubel Aklilu <kaklilu@chromium.org>
Commit-Queue: Matt Reichhoff <mreichhoff@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1187930}