Reland "Implement Fluent thumb painting on compositor thread."

The CL was reverted due to sanitizer tests failing. The cause for the
failure was due to not initializing two new variable in
in some tests. To see the fix, please see the changes from
patch 1 to 4 in this CL. I also scheduled linux and windows msan and
asan bot test runs in this CL.
Most *san runs I've scheduled are failing due to infra failures, but
linux_chromium_msan_rel_ng, which was one of the original failing
builds has passed.

This is a reland of commit d264772d90b43ac3aecb274963b63841ed264efd

Original change's description:
> Implement Fluent thumb painting on compositor thread.
>
> This CL reworks the way Fluent scrollbar thumbs are painted. The thumb
> for composited scrollbars will now be painted entirely in the compositor
> thread by creating a SolidColorDrawQuad and applying a mask to it to
> get the desired rounded corners. Drawing the scrollbar this way we
> avoid generating a bitmap for the thumb and re-painting every time
> the thumb's state changes (mouse over, press, overlay minimal mode,
> etc.).
>
> In order to get the correct color to the compositor thread a new
> function was declared to query the thumb's color from the Scrollbar,
> which is piped from the NativeTheme through the ScrollbarTheme.
> This function could easily be generalized to return the color of
> different parts, but since that behavior is not needed at the moment
> the function is scoped to scrollbar thumbs.
>
>
> Bug: 343942712
> Change-Id: I3fc35a13c01cb60d72fee1949a38adeb6fe8996a
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5595110
> Reviewed-by: Peter Kasting <pkasting@chromium.org>
> Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
> Commit-Queue: Gaston Rodriguez <gastonr@microsoft.com>
> Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1316727}

Bug: 343942712
Change-Id: Ic32e20d3fe97dfe7993e60b99ea5c8ed5129ca5e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5642992
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Reviewed-by: Yaroslav Shalivskyy <yshalivskyy@microsoft.com>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Gaston Rodriguez <gastonr@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#1320008}