Introduce MetaRenderer

MetaRenderer is meant to be the object responsible for rendering the
scene graph. It will contain the logic related to the cogl winsys
backend, the clutter backend, and the clutter stage window.

https://bugzilla.gnome.org/show_bug.cgi?id=768976

src/backends/meta-backend.c

@@ -63,6 +63,7 @@ struct _MetaBackendPrivate
   MetaMonitorManager *monitor_manager;
   MetaCursorRenderer *cursor_renderer;
   MetaInputSettings *input_settings;
+  MetaRenderer *renderer;
 
   ClutterBackend *clutter_backend;
   ClutterActor *stage;
@@ -371,11 +372,21 @@ meta_backend_real_get_relative_motion_deltas (MetaBackend *backend,
   return FALSE;
 }
 
+static void
+meta_backend_constructed (GObject *object)
+{
+  MetaBackend *backend = META_BACKEND (object);
+  MetaBackendPrivate *priv = meta_backend_get_instance_private (backend);
+
+  priv->renderer = META_BACKEND_GET_CLASS (backend)->create_renderer (backend);
+}
+
 static void
 meta_backend_class_init (MetaBackendClass *klass)
 {
   GObjectClass *object_class = G_OBJECT_CLASS (klass);
 
+  object_class->constructed = meta_backend_constructed;
   object_class->finalize = meta_backend_finalize;
 
   klass->post_init = meta_backend_real_post_init;
@@ -450,6 +461,16 @@ meta_backend_get_cursor_renderer (MetaBackend *backend)
   return priv->cursor_renderer;
 }
 
+/**
+ * meta_backend_get_renderer: (skip)
+ */
+MetaRenderer * meta_backend_get_renderer (MetaBackend *backend)
+{
+  MetaBackendPrivate *priv = meta_backend_get_instance_private (backend);
+
+  return priv->renderer;
+}
+
 /**
  * meta_backend_grab_device: (skip)
  */