[gnome-games] ui: Add HeaderBarWidget

[Alexander Mikhaylenko <alexm src gnome org>]

commit 0c720e5616105e783aac03f7d65c8fdfff363c9a
Author: sevagen <sevagenv gmail com>
Date:   Tue Feb 18 13:23:11 2020 +0530

    ui: Add HeaderBarWidget
    
    This interface will allow extra widgets added by plugins to block headerbar
    autohide when they have open popovers.

 src/core/header-bar-widget.vala | 5 +++++
 src/meson.build                 | 1 +
 2 files changed, 6 insertions(+)
---
diff --git a/src/core/header-bar-widget.vala b/src/core/header-bar-widget.vala
new file mode 100644
index 00000000..ecbde676
--- /dev/null
+++ b/src/core/header-bar-widget.vala
@@ -0,0 +1,5 @@
+// This file is part of GNOME Games. License: GPL-3.0+.
+
+public interface Games.HeaderBarWidget : Gtk.Widget {
+       public abstract bool block_autohide { get; }
+}
diff --git a/src/meson.build b/src/meson.build
index 6672c2bb..fb5cd0b8 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -21,6 +21,7 @@ vala_sources = [
   'core/game-collection.vala',
   'core/game-model.vala',
   'core/game-uri-adapter.vala',
+  'core/header-bar-widget.vala',
   'core/icon.vala',
   'core/input-capabilities.vala',
   'core/input-mode.vala',