[HarfBuzz] optimization for ASCII-only text

[Behdad Esfahbod]

On 08/09/2012 02:42 PM, Jonathan Kew wrote:

> Right, it's the cmap lookup that costs the time here (and if we can make our
> GetGlyph callback faster, that'd help too). So if map_glyphs can be combined
> with the check that normalization is doing, that should be equally effective.
> Maybe not quite as trivial to implement, but by all means, go for it! :)

Done.  Let me know how it performs.

behdad