[Profiles] Use new colored default avatars for taskbar badges

Recently, all logic around profile avatars has been integrated into
ProfileAttributesEntry::GetAvatarIcon() incl. new features such as
colored default avatars.

This CL updates code that generates taskbar badges on Windows to
delegate most of its logic to GetAvatarIcon(). Only the pieces needed
for obtaining ImageLoadStatus remained in this code.

The only behavioral change is for non-GAIA avatars: high-res /
2x windows old avatars are returned instead of low-res avatars. This
means more downscaling is needed than before. This will be addressed
by further CLs that will make GetAvatarIcon() respect preferred_size in
more cases.

Bug: 1122559
Change-Id: I5eecc7c6647dc78f9ff92d74edb64214a48e8e63
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2514153


Commit-Queue: Jan Krcal <jkrcal@chromium.org>
Reviewed-by: David Roger <droger@chromium.org>
Auto-Submit: Jan Krcal <jkrcal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824494}