[gnome-music/wip/jfelder/headerbar-devel-style] headerbar: Restore the devel style

[Jean Felder <jfelder src gnome org>]

commit 9c393fa5b9537041cc4def940f1c96f7346a22f7
Author: Jean Felder <jfelder src gnome org>
Date:   Wed Nov 6 23:44:26 2019 +0100

    headerbar: Restore the devel style
    
    When using the development version, the headerbar is supposed to have
    a custom style (to distinguish it from the stable version).
    
    However, with the introduction of the headerbar stack, this
    styling was lost. Indeed, the css rule assumes that the headerbar has
    the titlebar class, but, only the headerbar stack has it.
    
    This issue is fixed by adding the titlebar style to HeaderBar and
    SearchHeaderBar.

 data/ui/HeaderBar.ui       | 3 +++
 data/ui/SearchHeaderBar.ui | 3 +++
 2 files changed, 6 insertions(+)
---
diff --git a/data/ui/HeaderBar.ui b/data/ui/HeaderBar.ui
index bf04a328..d24359f8 100644
--- a/data/ui/HeaderBar.ui
+++ b/data/ui/HeaderBar.ui
@@ -4,6 +4,9 @@
   <template class="HeaderBar" parent="GtkHeaderBar">
     <property name="visible">True</property>
     <property name="vexpand">False</property>
+    <style>
+      <class name="titlebar"/>
+    </style>
     <child>
       <object class="GtkMenuButton" id="_menu_button">
         <property name="visible">True</property>
diff --git a/data/ui/SearchHeaderBar.ui b/data/ui/SearchHeaderBar.ui
index f837dae3..b894dbf2 100644
--- a/data/ui/SearchHeaderBar.ui
+++ b/data/ui/SearchHeaderBar.ui
@@ -4,6 +4,9 @@
   <template class="SearchHeaderBar" parent="GtkHeaderBar">
     <property name="visible">True</property>
     <property name="vexpand">False</property>
+    <style>
+      <class name="titlebar"/>
+    </style>
     <child>
       <object class="GtkToggleButton" id="_select_button">
         <property name="visible">True</property>