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

ash/system/tray/system_tray.cc

Index: ash/system/tray/system_tray.cc
diff --git a/ash/system/tray/system_tray.cc b/ash/system/tray/system_tray.cc
index 5c963cfa8aa7af48dd5e6bc1cf456edc6ba9398f..1857750663c6b295dcfe12487dcf2db4bf586afa 100644
--- a/ash/system/tray/system_tray.cc
+++ b/ash/system/tray/system_tray.cc
@@ -64,6 +64,7 @@
 #include "ui/gfx/skia_util.h"
 #include "ui/message_center/message_center.h"
 #include "ui/message_center/message_center_style.h"
+#include "ui/native_theme/native_theme.h"
 #include "ui/views/border.h"
 #include "ui/views/controls/label.h"
 #include "ui/views/view.h"
@@ -472,7 +473,6 @@ void SystemTray::ShowItems(const std::vector<SystemTrayItem*>& items,
       // This is the case where a volume control or brightness control bubble
       // is created.
       init_params.max_height = default_bubble_height_;
-      init_params.bg_color = kBackgroundColor;
     } else {
       init_params.bg_color = kHeaderBackgroundColor;
     }