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..8319c32ff50cd4481e57d3cae38d8416ba2ac9f6 100644
--- a/ash/system/audio/volume_view.cc
+++ b/ash/system/audio/volume_view.cc
@@ -130,7 +130,8 @@ 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);