Pass ScrollableArea ColorScheme for scrollbar painting.

Bug: 939811
Change-Id: I17964cd5d3dbfd699103f645b7a9ec45c46e0579
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1742148
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Reviewed-by: Mason Freed <masonfreed@chromium.org>
Cr-Commit-Position: refs/heads/master@{#686750}
10 files changed