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

ash/system/tray_accessibility.cc

Index: ash/system/tray_accessibility.cc
diff --git a/ash/system/tray_accessibility.cc b/ash/system/tray_accessibility.cc
index 3d042c2f7fa4aea67d472200aa7e294df7dbea19..c2c6215dc7410a845ce4fafe24c543aee81ec7d4 100644
--- a/ash/system/tray_accessibility.cc
+++ b/ash/system/tray_accessibility.cc
@@ -130,7 +130,8 @@ AccessibilityPopupView::AccessibilityPopupView(uint32_t enabled_state_bits)
     : label_(CreateLabel(enabled_state_bits)) {}
 
 void AccessibilityPopupView::Init() {
-  set_background(views::Background::CreateSolidBackground(kBackgroundColor));
+  set_background(views::Background::CreateThemedSolidBackground(
+      this, ui::NativeTheme::kColorId_BubbleBackground));
 
   views::GridLayout* layout = new views::GridLayout(this);
   SetLayoutManager(layout);