st: Adjust theme test

Mutter's Clutter fork can no longer be initialized separatedly, as
its backend now draws from MetaBackend. Adjust the code to use the
newly added test initialization function instead to get the test
back up.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/691

src/st/meson.build

@@ -136,7 +136,7 @@ libst_dep = declare_dependency(link_with: libst,
 test_theme = executable('test-theme',
   sources: 'test-theme.c',
   c_args: st_cflags,
-  dependencies: [clutter_dep, gtk_dep],
+  dependencies: [mutter_dep, gtk_dep],
   build_rpath: mutter_typelibdir,
   link_with: libst
 )

src/st/test-theme.c

@@ -25,6 +25,7 @@
 #include "st-button.h"
 #include <math.h>
 #include <string.h>
+#include <meta/main.h>
 
 static ClutterActor *stage;
 static StThemeNode *root;
@@ -536,11 +537,16 @@ main (int argc, char **argv)
   StThemeContext *context;
   PangoFontDescription *font_desc;
   GFile *file;
+  g_autofree char *cwd = NULL;
 
   gtk_init (&argc, &argv);
 
-  if (clutter_init (&argc, &argv) != CLUTTER_INIT_SUCCESS)
-    return 1;
+  /* meta_init() cds to $HOME */
+  cwd = g_get_current_dir ();
+
+  meta_test_init ();
+
+  chdir (cwd);
 
   /* Make sure our assumptions about resolution are correct */
   g_object_set (clutter_settings_get_default (), "font-dpi", -1, NULL);