MetaPlugin: add a size_changed vfunc

This will be used to let plugins know when a previous size change
actually becomes effective. This is needed to handle wayland client
resizing properly since, unlike X, it's async.

https://bugzilla.gnome.org/show_bug.cgi?id=770345

src/compositor/meta-plugin-manager.c

@@ -202,6 +202,17 @@ meta_plugin_manager_event_simple (MetaPluginManager *plugin_mgr,
   return retval;
 }
 
+void
+meta_plugin_manager_event_size_changed (MetaPluginManager *plugin_mgr,
+                                        MetaWindowActor   *actor)
+{
+  MetaPlugin *plugin = plugin_mgr->plugin;
+  MetaPluginClass *klass = META_PLUGIN_GET_CLASS (plugin);
+
+  if (klass->size_changed)
+    klass->size_changed (plugin, actor);
+}
+
 gboolean
 meta_plugin_manager_event_size_change (MetaPluginManager *plugin_mgr,
                                        MetaWindowActor   *actor,

src/compositor/meta-plugin-manager.h

@@ -50,6 +50,9 @@ gboolean meta_plugin_manager_event_simple (MetaPluginManager *mgr,
                                            MetaWindowActor   *actor,
                                            MetaPluginEffect   event);
 
+void     meta_plugin_manager_event_size_changed   (MetaPluginManager *mgr,
+                                                   MetaWindowActor   *actor);
+
 gboolean meta_plugin_manager_event_size_change    (MetaPluginManager *mgr,
                                                    MetaWindowActor   *actor,
                                                    MetaSizeChange     which_change,

src/meta/meta-plugin.h

@@ -102,6 +102,9 @@ struct _MetaPluginClass
   void (*unminimize)       (MetaPlugin         *plugin,
                             MetaWindowActor    *actor);
 
+  void (*size_changed)     (MetaPlugin         *plugin,
+                            MetaWindowActor    *actor);
+
   void (*size_change)      (MetaPlugin         *plugin,
                             MetaWindowActor    *actor,
                             MetaSizeChange      which_change,