views: repaint BubbleFrameView when changing background color

This is much more necessary with the view repaint optimization enabled
via the EnableViewPaintOptimization feature. Without that optimization,
the BubbleFrameView was getting repainted by accident: usually a
control in the bubble would change in response to a theme change, and
that would damage the BubbleFrameView's bounds rect, which would cause
a repaint of the BubbleFrameView.

Bug: 999208
Change-Id: Ia71d5e7474a00971502a87dcc2d9cea7c4368853
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1774787
Auto-Submit: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Bret Sepulveda <bsep@chromium.org>
Reviewed-by: Bret Sepulveda <bsep@chromium.org>
Cr-Commit-Position: refs/heads/master@{#692177}

ui/views/bubble/bubble_frame_view.cc

@@ -466,6 +466,7 @@ void BubbleFrameView::SetArrow(BubbleBorder::Arrow arrow) {
 
 void BubbleFrameView::SetBackgroundColor(SkColor color) {
   bubble_border_->set_background_color(color);
+  SchedulePaint();
 }
 
 gfx::Rect BubbleFrameView::GetUpdatedWindowBounds(