Comment 19 for bug 193108

Thanks, David. Yes it looks like pango_fc_font_find_shaper should use
pango_map_get_engines and _pango_engine_shape_covers like get_shaper_and_font
in pango-context.c.

However gfxPangoFont::GetCharSize is not being used for complex characters and
so could(/should) just use pango_font_get_glyph_extents.