special-case edge-building for polygons (paths with only lines)

special-case edge-building for polygons (paths with only lines)
makes the dashing bench faster (from 13.4 -> 11.5 ticks)
Committed: https://code.google.com/p/skia/source/detail?r=4916

[reed1, 2012-08-01 21:49:28]

Key seems to be:
- remove overhead of using chunkalloc.alloc() per-edge
- remove overhead of growing/checking fList on each append

Downsides:
- we can often allocate more than needed (e.g. if a lot of edges are discarded
if setEdge returns false)

Other improvements:
- can I skip calling the SkPath::Iter, esp. in this simple case?
- can/should any of these changes be applied in the general case?

[bsalomon, 2012-08-02 13:40:26]

On 2012/08/01 21:49:28, reed1 wrote:
> Key seems to be:
> - remove overhead of using chunkalloc.alloc() per-edge
> - remove overhead of growing/checking fList on each append
> 
> Downsides:
> - we can often allocate more than needed (e.g. if a lot of edges are discarded
> if setEdge returns false)
> 
> Other improvements:
> - can I skip calling the SkPath::Iter, esp. in this simple case?
> - can/should any of these changes be applied in the general case?

The parts I understand LGTM. It does seems like we could have a fast line-only
iterator.