Introduced the notification header

In the new grouping model we don't have a dedicated expand button
anymore but only the notification header.

Bug: 24866646
Change-Id: I2e4bc82e502fde951a71b61cd81347c44b9637f6
diff --git a/packages/SystemUI/res/values/styles.xml b/packages/SystemUI/res/values/styles.xml
index 8241ddf..9e942f0 100644
--- a/packages/SystemUI/res/values/styles.xml
+++ b/packages/SystemUI/res/values/styles.xml
@@ -244,6 +244,10 @@
         <item name="android:textColor">#60000000</item>
     </style>
 
+    <style name="TextAppearance.Material.Notification.HeaderTitle"
+        parent="@*android:style/TextAppearance.Material.Notification.Info">
+    </style>
+
     <style name="SearchPanelCircle">
         <item name="android:layout_width">match_parent</item>
         <item name="android:layout_height">match_parent</item>