[mutter] DisplayConfig: Add 'supports-changing-layout-mode' property

[Jonas Ådahl <jadahl src gnome org>]

commit bdcb395b3343864d3be8a2447e394250baf41b92
Author: Jonas Ådahl <jadahl gmail com>
Date:   Thu Apr 6 14:00:06 2017 +0800

    DisplayConfig: Add 'supports-changing-layout-mode' property
    
    This property may be used by a client to determine whether it is
    allowed to change the layout mode.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=777732

 src/backends/meta-monitor-manager.c    |    7 +++++--
 src/org.gnome.Mutter.DisplayConfig.xml |    3 +++
 2 files changed, 8 insertions(+), 2 deletions(-)
---
diff --git a/src/backends/meta-monitor-manager.c b/src/backends/meta-monitor-manager.c
index 48c99a0..5104d73 100644
--- a/src/backends/meta-monitor-manager.c
+++ b/src/backends/meta-monitor-manager.c
@@ -1531,11 +1531,14 @@ meta_monitor_manager_handle_get_current_state (MetaDBusDisplayConfig *skeleton,
                              g_variant_new_boolean (FALSE));
     }
 
+  g_variant_builder_add (&properties_builder, "{sv}",
+                         "layout-mode",
+                         g_variant_new_uint32 (manager->layout_mode));
   if (capabilities & META_MONITOR_MANAGER_CAPABILITY_LAYOUT_MODE)
     {
       g_variant_builder_add (&properties_builder, "{sv}",
-                             "layout-mode",
-                             g_variant_new_uint32 (manager->layout_mode));
+                             "supports-changing-layout-mode",
+                             g_variant_new_boolean (TRUE));
     }
 
   if (meta_monitor_manager_get_max_screen_size (manager,
diff --git a/src/org.gnome.Mutter.DisplayConfig.xml b/src/org.gnome.Mutter.DisplayConfig.xml
index 5b54438..30d2ead 100644
--- a/src/org.gnome.Mutter.DisplayConfig.xml
+++ b/src/org.gnome.Mutter.DisplayConfig.xml
@@ -398,6 +398,9 @@
                             using the logical monitor scale.
            * 2 : physical - the dimension of a logical monitor is derived from
                             the monitor modes associated with it.
+       * "supports-changing-layout-mode" (b): True if the layout mode can be
+                                              changed. Absence of this means the
+                                              layout mode cannot be changed.
     -->
     <method name="GetCurrentState">
       <arg name="serial" direction="out" type="u" />