Modifies triangle corner shaders to just approximate their coverage with
linear values that ramp to zero at bloat vertices outside the triangle.
For the vertex backend, since corners now have the same fragment shader
as the rest of the triangle, we fold them in with the other steps and
draw triangles in a single pass.
The geometry backend still draws triangles in two passes, as there is
not an apparent performance advantage in combining them.
Bug: skia:
Change-Id: Ib4a89d793a3c706f734d0271875c8a3e5c87c49b
Reviewed-on: https://skia-review.googlesource.com/112632
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
622650a194