Coverage counting path renderer

Initial implementation of a GPU path renderer that draws antialiased
paths by counting coverage in an offscreen buffer.

Initially disabled until it has had time to soak.

Bug: skia:
Change-Id: I003d8cfdf8dc62641581b5ea2dc4f0aa00108df6
Commit-Queue: Chris Dalton <>
Reviewed-by: Greg Daniel <>
Reviewed-by: Brian Salomon <>
Reviewed-by: Robert Phillips <>
24 files changed