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

ui/views/bubble/tray_bubble_view.h

Index: ui/views/bubble/tray_bubble_view.h
diff --git a/ui/views/bubble/tray_bubble_view.h b/ui/views/bubble/tray_bubble_view.h
index 12b9bad4709cbc68aff3c371cd0604060dc19bd0..8de9c3053ed8a920002c80f5dd90987bff1ae8f3 100644
--- a/ui/views/bubble/tray_bubble_view.h
+++ b/ui/views/bubble/tray_bubble_view.h
@@ -8,7 +8,6 @@
 #include <memory>
 
 #include "base/macros.h"
-#include "base/optional.h"
 #include "ui/views/bubble/bubble_dialog_delegate.h"
 #include "ui/views/mouse_watcher.h"
 #include "ui/views/views_export.h"
@@ -84,8 +83,7 @@
     int max_height;
     bool can_activate;
     bool close_on_deactivate;
-    // If not provided, the bg color will be derived from the NativeTheme.
-    base::Optional<SkColor> bg_color;
+    SkColor bg_color;
   };
 
   // Constructs and returns a TrayBubbleView. |init_params| may be modified.