Implement user-visible latency metrics for minor mode compliance.

Tracks the latency added to sync screens by loading the account
capabilities - effectively, the duration and presence of ui wait
elements like spinners or throbblers.

The metric is already implemented for Android and iOS and this CL is
adding the implementation for desktop.

See
//tools/metrics/histograms/metadata/signin/histograms.xml:://histogram[@name="Signin.AccountCapabilities.*"]
for details.

Bug: b:318349268
Change-Id: I63db80ac6b302057410d501e73d9b59f9e2233bc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5272454
Auto-Submit: Tomek Jurkiewicz <tju@google.com>
Commit-Queue: Tomek Jurkiewicz <tju@google.com>
Reviewed-by: Alex Ilin <alexilin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1259797}