This patch converts sky.Paint to be a pure Dart object, which means we don't
need to open a weak handle to sky.Paint. Avoiding the weak handle reduces the
amount of weak handle callbacks we need to process at the end of GC and
therefore reduces jank.
This is supposed to make Viktor's game faster, but it's not clear
to me that it actually does. I've left the code
using the dart version of drawAtlas for now until Viktor can
verify that it looks correct.
I also added a wrapper for SkFilterQuality in the process of
debugging SkCanvas.drawAtlas since all drawAtlas examples
in Skia use FilterQuality.low. The bug which blocked me for
so long turned out to be that SkCanvas.drawAtlas doesn't
draw anything if antialiasing is turned on.
Issue #138.
R=abarth@google.com
