[Cairo] Color transforms

[Keith Packard]

Around 9 o'clock on Jul 19, Owen Taylor wrote:

> This operation hasn't shown up to be much of a bottleneck for Pango;
> it's the mapping from pattern => list of fonts that we needed to
> cache aggressively.

Then I'll certainly cache that -- I can also tell when the configuration 
has changed and invalidate the cache.

> I'm pretty sure we'll be going to non-local glyph selection for Pango
> in the near future to get punctuation/whitespace/etc from the right
> font, so a character => font cache isn't going to be useful
> for Pango.

Ok, so I guess we should profile things before I go implementing a lot of 
unnecessary optimizations...

-keith