Update from https://crrev.com/316786

third_party/harfbuzz-ng/src/hb-ft.h

 /*
  * Copyright © 2009  Red Hat, Inc.
  *
  *  This is part of HarfBuzz, a text shaping library.
  *
  * Permission is hereby granted, without written agreement and without
  * license or royalty fees, to use, copy, modify, and distribute this
  * software and its documentation for any purpose, provided that the
  * above copyright notice and the following two paragraphs appear in
  * all copies of this software.
@@ skipping 16 matching lines @@
 #ifndef HB_FT_H
 #define HB_FT_H
 
 #include "hb.h"
 
 #include <ft2build.h>
 #include FT_FREETYPE_H
 
 HB_BEGIN_DECLS
 
-/* Note: FreeType is not thread-safe.  Hence, these functions are not either. */
+/*
+ * Note: FreeType is not thread-safe.
+ * Hence, these functions are not either.
+ */
 
+/*
+ * hb-face from ft-face.
+ */
+
+/* This one creates a new hb-face for given ft-face.
+ * When the returned hb-face is destroyed, the destroy
+ * callback is called (if not NULL), with the ft-face passed
+ * to it.
+ *
+ * The client is responsible to make sure that ft-face is
+ * destroyed after hb-face is destroyed.
+ *
+ * Most often you don't want this function.  You should use either
+ * hb_ft_face_create_cached(), or hb_ft_face_create_referenced().
+ * In particular, if you are going to pass NULL as destroy, you
+ * probably should use (the more recent) hb_ft_face_create_referenced()
+ * instead.
+ */
 hb_face_t *
 hb_ft_face_create (FT_Face           ft_face,
                    hb_destroy_func_t destroy);
 
+/* This version is like hb_ft_face_create(), except that it caches
+ * the hb-face using the generic pointer of the ft-face.  This means
+ * that subsequent calls to this function with the same ft-face will
+ * return the same hb-face (correctly referenced).
+ *
+ * Client is still responsible for making sure that ft-face is destroyed
+ * after hb-face is.
+ */
 hb_face_t *
 hb_ft_face_create_cached (FT_Face ft_face);
 
+/* This version is like hb_ft_face_create(), except that it calls
+ * FT_Reference_Face() on ft-face, as such keeping ft-face alive
+ * as long as the hb-face is.
+ *
+ * This is the most convenient version to use.  Use it unless you have
+ * very good reasons not to.
+ */
+hb_face_t *
+hb_ft_face_create_referenced (FT_Face ft_face);
+
+
+/*
+ * hb-font from ft-face.
+ */
+
+/*
+ * Note:
+ *
+ * Set face size on ft-face before creating hb-font from it.
+ * Otherwise hb-ft would NOT pick up the font size correctly.
+ */
+
+/* See notes on hb_ft_face_create().  Same issues re lifecycle-management
+ * apply here.  Use hb_ft_font_create_referenced() if you can. */
 hb_font_t *
 hb_ft_font_create (FT_Face           ft_face,
                    hb_destroy_func_t destroy);
 
+/* See notes on hb_ft_face_create_referenced() re lifecycle-management
+ * issues. */
+hb_font_t *
+hb_ft_font_create_referenced (FT_Face ft_face);
 
 
 /* Makes an hb_font_t use FreeType internally to implement font functions. */
 void
 hb_ft_font_set_funcs (hb_font_t *font);
 
 FT_Face
 hb_ft_font_get_face (hb_font_t *font);
 
 
 HB_END_DECLS
 
 #endif /* HB_FT_H */