ttml: add refcounting to GstSubtitleStlyeSet type

https://bugzilla.gnome.org/show_bug.cgi?id=780402

ext/ttml/gstttmlrender.c

@@ -1242,7 +1242,7 @@ map_fail:
 
 typedef struct
 {
-  const GstSubtitleElement *element;
+  GstSubtitleElement *element;
   gchar *text;
 } UnifiedElement;
 

ext/ttml/subtitle.c

@@ -32,6 +32,22 @@
 
 #include "subtitle.h"
 
+/**
+ * gst_subtitle_style_set_free:
+ * @style_set: A #GstSubtitleStyleSet.
+ *
+ * Free @style_set and its associated memory.
+ */
+static void
+_gst_subtitle_style_set_free (GstSubtitleStyleSet * style_set)
+{
+  g_return_if_fail (style_set != NULL);
+  g_free (style_set->font_family);
+  g_slice_free (GstSubtitleStyleSet, style_set);
+}
+
+GST_DEFINE_MINI_OBJECT_TYPE (GstSubtitleStyleSet, gst_subtitle_style_set);
+
 /**
  * gst_subtitle_style_set_new:
  *
@@ -46,6 +62,10 @@ gst_subtitle_style_set_new (void)
   GstSubtitleColor white = { 255, 255, 255, 255 };
   GstSubtitleColor transparent = { 0, 0, 0, 0 };
 
+  gst_mini_object_init (GST_MINI_OBJECT_CAST (ret), 0,
+      gst_subtitle_style_set_get_type (), NULL, NULL,
+      (GstMiniObjectFreeFunction) _gst_subtitle_style_set_free);
+
   ret->font_family = g_strdup ("default");
   ret->font_size = 1.0;
   ret->line_height = 1.25;
@@ -60,26 +80,12 @@ gst_subtitle_style_set_new (void)
   return ret;
 }
 
-/**
- * gst_subtitle_style_set_free:
- * @style_set: A #GstSubtitleStyleSet.
- *
- * Free @style_set and its associated memory.
- */
-void
-gst_subtitle_style_set_free (GstSubtitleStyleSet * style_set)
-{
-  g_return_if_fail (style_set != NULL);
-  g_free (style_set->font_family);
-  g_slice_free (GstSubtitleStyleSet, style_set);
-}
-
 
 static void
 _gst_subtitle_element_free (GstSubtitleElement * element)
 {
   g_return_if_fail (element != NULL);
-  gst_subtitle_style_set_free (element->style_set);
+  gst_subtitle_style_set_unref (element->style_set);
   g_slice_free (GstSubtitleElement, element);
 }
 
@@ -121,7 +127,7 @@ static void
 _gst_subtitle_block_free (GstSubtitleBlock * block)
 {
   g_return_if_fail (block != NULL);
-  gst_subtitle_style_set_free (block->style_set);
+  gst_subtitle_style_set_unref (block->style_set);
   g_ptr_array_unref (block->elements);
   g_slice_free (GstSubtitleBlock, block);
 }
@@ -202,7 +208,7 @@ gst_subtitle_block_get_element_count (const GstSubtitleBlock * block)
  * function does not return a reference; the caller should obtain a reference
  * using gst_subtitle_element_ref(), if needed.
  */
-const GstSubtitleElement *
+GstSubtitleElement *
 gst_subtitle_block_get_element (const GstSubtitleBlock * block, guint index)
 {
   g_return_val_if_fail (block != NULL, NULL);
@@ -217,7 +223,7 @@ static void
 _gst_subtitle_region_free (GstSubtitleRegion * region)
 {
   g_return_if_fail (region != NULL);
-  gst_subtitle_style_set_free (region->style_set);
+  gst_subtitle_style_set_unref (region->style_set);
   g_ptr_array_unref (region->blocks);
   g_slice_free (GstSubtitleRegion, region);
 }

ext/ttml/subtitle.h

@@ -366,7 +366,10 @@ typedef enum {
  * all object types. The types to which each attribute applies is given in the
  * description of that attribute below.
  */
-struct _GstSubtitleStyleSet {
+struct _GstSubtitleStyleSet
+{
+  GstMiniObject mini_object;
+
   GstSubtitleTextDirection text_direction;
   gchar *font_family;
   gdouble font_size;
@@ -388,11 +391,42 @@ struct _GstSubtitleStyleSet {
   GstSubtitleWritingMode writing_mode;
   GstSubtitleBackgroundMode show_background;
   GstSubtitleOverflowMode overflow;
+
+  /*< private >*/
+  gpointer _gst_reserved[GST_PADDING];
 };
 
+GType gst_subtitle_style_set_get_type (void);
+
 GstSubtitleStyleSet * gst_subtitle_style_set_new (void);
 
-void gst_subtitle_style_set_free (GstSubtitleStyleSet * style_set);
+/**
+ * gst_subtitle_style_set_ref:
+ * @style_set: A #GstSubtitleStyleSet.
+ *
+ * Increments the refcount of @style_set.
+ *
+ * Returns: (transfer full): @style_set.
+ */
+static inline GstSubtitleStyleSet *
+gst_subtitle_style_set_ref (GstSubtitleStyleSet * style_set)
+{
+  return (GstSubtitleStyleSet *)
+    gst_mini_object_ref (GST_MINI_OBJECT_CAST (style_set));
+}
+
+/**
+ * gst_subtitle_style_set_unref:
+ * @style_set: (transfer full): A #GstSubtitleStyleSet.
+ *
+ * Decrements the refcount of @style_set. If the refcount reaches 0, @style_set
+ * will be freed.
+ */
+static inline void
+gst_subtitle_style_set_unref (GstSubtitleStyleSet * style_set)
+{
+  gst_mini_object_unref (GST_MINI_OBJECT_CAST (style_set));
+}
 
 
 /**
@@ -489,7 +523,7 @@ void gst_subtitle_block_add_element (
 
 guint gst_subtitle_block_get_element_count (const GstSubtitleBlock * block);
 
-const GstSubtitleElement * gst_subtitle_block_get_element (
+GstSubtitleElement * gst_subtitle_block_get_element (
     const GstSubtitleBlock * block, guint index);
 
 /**