1. @DomName('FontFaceSetForEachCallback')
  2. @Experimental()
void FontFaceSetForEachCallback(FontFace fontFace, FontFace fontFaceAgain, FontFaceSet set)

Emitted for any setlike IDL entry needs a callback signature. Today there is only one.

Source 

@DomName('FontFaceSetForEachCallback')
@Experimental() // untriaged
typedef void FontFaceSetForEachCallback(
    FontFace fontFace, FontFace fontFaceAgain, FontFaceSet set);