docs: add docs for GtkFrameClock

gdk/gdkframeclockprivate.h

@@ -31,6 +31,10 @@
 
 G_BEGIN_DECLS
 
+/**
+ * GdkFrameClock:
+ * @parent_instance: The parent instance.
+ */
 struct _GdkFrameClock
 {
   GObject parent_instance;
@@ -39,10 +43,24 @@ struct _GdkFrameClock
   GdkFrameClockPrivate *priv;
 };
 
+/**
+ * GdkFrameClockClass:
+ * @parent_class: The parent class.
+
+ * @get_frame_time: Gets the time that should currently be used for
+ *    animations.
+ * @request_phase: Asks the frame clock to run a particular phase.
+ * @begin_updating: Starts updates for an animation.
+ * @end_updating: Stops updates for an animation.
+ * @freeze: 
+ * @thaw: 
+ */
 struct _GdkFrameClockClass
 {
   GObjectClass parent_class;
 
+  /*< public >*/
+
   gint64   (* get_frame_time) (GdkFrameClock *clock);
 
   void     (* request_phase)  (GdkFrameClock      *clock,
@@ -65,6 +83,7 @@ struct _GdkFrameClockClass
 
 struct _GdkFrameTimings
 {
+  /*< private >*/
   guint ref_count;
 
   gint64 frame_counter;