Repaint scrollbars on preferredRootScrollbarColorScheme setting change

Switching between custom and default browser themes, or light and dark
browser color mode doesn't trigger the scrollbars paint invalidation on
some pages. This creates an inconsistent behavior for root scrollbars
that depend on the settings.

The CL fixes the issue by explicitly triggering a repaint for all
renderers whenever preferredRootScrollbarColorScheme setting value
changes.

Bug: 340178599
Change-Id: I9b26def18e4b095c3a2a61281406d31e75ebb47f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5541742
Reviewed-by: Gaston Rodriguez <gastonr@microsoft.com>
Reviewed-by: Olga Gerchikov <gerchiko@microsoft.com>
Reviewed-by: Alison Maher <almaher@microsoft.com>
Commit-Queue: Yaroslav Shalivskyy <yshalivskyy@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#1304801}