[cairo] [PATCH cairo] Drop the experimental skia backend

[Chris Wilson]

Quoting Bryce Harrington (2017-08-21 22:47:21)
> As has been stated in the README, skia is not API stable and is not
> available packaged, versioned forms, resulting in it being a continually
> moving target.  So the cairo skia backend has to be updated continually
> as the skia API morphs, which means in practice that Cairo's skia
> backend will always work only with a specific snapshot and lacking a
> high degree of maintenance activity will always be badly out of date.
> The last time the cairo skia backend was updated was in 2014, and had
> not been updated very regularly prior to that.
> 
> While this was an interesting experiment, it is probably better to
> recommend that people interested in Skia capabilities just use Skia
> directly.

? It's target is you, the cairo developer, to compare against the things
that skia does better whilst being constrained to the same pdl as cairo.
Hence experimental. Carrying it should have very little maintenance
burden (since it is not marked as being maintained), yet reduce the cost
of such experiments by allowing/encouraging collaboration

Skia is smarter at handling splines, tight generation of rasterisers and
sources (benefiting from having its pixman integration). In short, it
does a lot better than Cairo in many circumstances; where Cairo used to
have an advantage was areas such as decomposing paths in faster
primitives, pixman had more acceleration paths.
-Chris