Update from https://crrev.com/316786

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

Index: third_party/harfbuzz-ng/src/hb-ft.h
diff --git a/third_party/harfbuzz-ng/src/hb-ft.h b/third_party/harfbuzz-ng/src/hb-ft.h
index 696251e143f31987eb599f8cb16db4f12ff8d901..92f4b3614415503a939da9409b3794d85e7d7b7b 100644
--- a/third_party/harfbuzz-ng/src/hb-ft.h
+++ b/third_party/harfbuzz-ng/src/hb-ft.h
@@ -34,19 +34,76 @@
 
 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. */