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

ash/system/audio/volume_view.cc

Index: ash/system/audio/volume_view.cc
diff --git a/ash/system/audio/volume_view.cc b/ash/system/audio/volume_view.cc
index 7fdf5711016736597436a6cb70f733c2be3d2804..62896bae6693c1d5f04daeb80bc15e17b60f1eb1 100644
--- a/ash/system/audio/volume_view.cc
+++ b/ash/system/audio/volume_view.cc
@@ -20,6 +20,7 @@
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/gfx/paint_vector_icon.h"
 #include "ui/gfx/vector_icon_types.h"
+#include "ui/native_theme/native_theme.h"
 #include "ui/views/background.h"
 #include "ui/views/border.h"
 #include "ui/views/controls/button/custom_button.h"
@@ -130,7 +131,8 @@ VolumeView::VolumeView(SystemTrayItem* owner,
       l10n_util::GetStringUTF16(IDS_ASH_STATUS_TRAY_VOLUME));
   tri_view_->AddView(TriView::Container::CENTER, slider_);
 
-  set_background(views::Background::CreateSolidBackground(kBackgroundColor));
+  set_background(views::Background::CreateThemedSolidBackground(
+      this, ui::NativeTheme::kColorId_BubbleBackground));
 
   if (!is_default_view_) {
     tri_view_->SetContainerVisible(TriView::Container::END, false);