[mutter] tests/clutter: Disable X11 client support

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit f57c39f511a7353b3e03e05326672c016ab22da6
Author: Jonas Ådahl <jadahl gmail com>
Date:   Sun Nov 8 22:02:39 2020 +0100

    tests/clutter: Disable X11 client support
    
    This avoids test failure happening due to Xwayland getting the CPU time
    instead of the tests themself, causing failures e.g. due to
    missing frames.
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1555

 src/core/main-private.h        |  3 +++
 src/core/main.c                | 11 +++++++++++
 src/tests/clutter-test-utils.c |  2 ++
 3 files changed, 16 insertions(+)
---
diff --git a/src/core/main-private.h b/src/core/main-private.h
index c37ce8cd62..210fe6289d 100644
--- a/src/core/main-private.h
+++ b/src/core/main-private.h
@@ -51,6 +51,9 @@ void meta_override_compositor_configuration (MetaCompositorType compositor_type,
 
 MetaDisplayPolicy meta_get_x11_display_policy (void);
 
+META_EXPORT_TEST
+void meta_override_x11_display_policy (MetaDisplayPolicy x11_display_policy);
+
 META_EXPORT_TEST
 void meta_start (void);
 
diff --git a/src/core/main.c b/src/core/main.c
index e68f3c9edd..7c936a3a64 100644
--- a/src/core/main.c
+++ b/src/core/main.c
@@ -772,6 +772,14 @@ prefs_changed_callback (MetaPreference pref,
     }
 }
 
+static MetaDisplayPolicy x11_display_policy_override = -1;
+
+void
+meta_override_x11_display_policy (MetaDisplayPolicy x11_display_policy)
+{
+  x11_display_policy_override = x11_display_policy;
+}
+
 MetaDisplayPolicy
 meta_get_x11_display_policy (void)
 {
@@ -780,6 +788,9 @@ meta_get_x11_display_policy (void)
   if (META_IS_BACKEND_X11_CM (backend))
     return META_DISPLAY_POLICY_MANDATORY;
 
+  if (x11_display_policy_override != -1)
+    return x11_display_policy_override;
+
 #ifdef HAVE_WAYLAND
   if (meta_is_wayland_compositor ())
     {
diff --git a/src/tests/clutter-test-utils.c b/src/tests/clutter-test-utils.c
index 84701e2048..4e18edbedb 100644
--- a/src/tests/clutter-test-utils.c
+++ b/src/tests/clutter-test-utils.c
@@ -5,6 +5,7 @@
 #include <clutter/clutter.h>
 
 #include "compositor/meta-plugin-manager.h"
+#include "core/main-private.h"
 
 typedef struct {
   gpointer dummy_field;
@@ -50,6 +51,7 @@ init_common_pre (void)
              "aborting...\n");
 
   meta_plugin_manager_load (test_get_plugin_name ());
+  meta_override_x11_display_policy (META_DISPLAY_POLICY_DISABLED);
   meta_test_init ();
 
   display = g_getenv ("DISPLAY");