[cbdt] Rename reference_blob_for_glyph() to reference_png()

src/hb-ot-color-cbdt-table.hh

@@ -504,12 +504,12 @@ struct CBDT
       }
     }
 
-    inline hb_blob_t* reference_blob_for_glyph (hb_codepoint_t  glyph_id,
-						unsigned int    x_ppem,
-						unsigned int    y_ppem) const
+    inline hb_blob_t* reference_png (hb_codepoint_t  glyph_id,
+				     unsigned int    x_ppem,
+				     unsigned int    y_ppem) const
     {
       if (!cblc)
-	return hb_blob_get_empty ();  // Not a color bitmap font.
+	return hb_blob_get_empty ();
 
       if (x_ppem == 0) x_ppem = upem;
       if (y_ppem == 0) y_ppem = upem;

src/hb-ot-color.cc

@@ -321,7 +321,7 @@ hb_ot_color_glyph_reference_png (hb_font_t *font, hb_codepoint_t  glyph)
     blob = _get_sbix (font->face).reference_png (font, glyph, nullptr, nullptr);
 
   if (hb_blob_get_length (blob) == 0 && _get_cbdt (font->face).has_data ())
-    blob = _get_cbdt (font->face).reference_blob_for_glyph (glyph, font->x_ppem, font->y_ppem);
+    blob = _get_cbdt (font->face).reference_png (glyph, font->x_ppem, font->y_ppem);
 
   return blob;
 }