Introduce a type of View background that stays in sync with its host

ui/views/bubble/tray_bubble_view.cc

Index: ui/views/bubble/tray_bubble_view.cc
diff --git a/ui/views/bubble/tray_bubble_view.cc b/ui/views/bubble/tray_bubble_view.cc
index 3d7a93eecae09d4b4d6f03ab71aef2e27a33c54c..e1cd28571acad798e53ce195d56e7f571c3e17bb 100644
--- a/ui/views/bubble/tray_bubble_view.cc
+++ b/ui/views/bubble/tray_bubble_view.cc
@@ -175,8 +175,7 @@ TrayBubbleView::InitParams::InitParams(AnchorAlignment anchor_alignment,
       max_width(max_width),
       max_height(0),
       can_activate(false),
-      close_on_deactivate(true),
-      bg_color(gfx::kPlaceholderColor) {}
+      close_on_deactivate(true) {}
 
 TrayBubbleView::InitParams::InitParams(const InitParams& other) = default;
 
@@ -196,12 +195,14 @@ TrayBubbleView::TrayBubbleView(View* anchor,
       layout_(new BottomAlignedBoxLayout(this)),
       delegate_(delegate),
       preferred_width_(init_params.min_width),
-      bubble_border_(new BubbleBorder(arrow(),
-                                      BubbleBorder::NO_ASSETS,
-                                      init_params.bg_color)),
+      bubble_border_(new BubbleBorder(
+          arrow(),
+          BubbleBorder::NO_ASSETS,
+          init_params.bg_color.value_or(gfx::kPlaceholderColor))),
       owned_bubble_border_(bubble_border_),
       is_gesture_dragging_(false),
       mouse_actively_entered_(false) {
+  bubble_border_->set_use_theme_background_color(!init_params.bg_color);
   bubble_border_->set_alignment(BubbleBorder::ALIGN_EDGE_TO_ANCHOR_EDGE);
   bubble_border_->set_paint_arrow(BubbleBorder::PAINT_NONE);
   set_can_activate(params_.can_activate);