[SkiaFontService 4/4] Override default font manager when applicable

Previous CLs in the relation chain are just defining the classes.
This CL enables the binding and override of the font manager.

Override the default font manager if all are true:
   a) URL is a TopChrome WebUI.
   b) Running on Windows.
   c) SkiaFontService feature flag is enabled.

Low-Coverage-Reason: COVERAGE_UNDERREPORTED
Bug: 335680565
Change-Id: I03beeacf65b44290d1802522daf1fb6dc6703496
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5548570
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Greg Thompson <grt@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Commit-Queue: David Yeung <dayeung@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1316680}