We had a remarkable number of analyzer failures.
I'll fix the bots to analyze across the whole project
in a follow-up patch, that should prevent this
in the future.
@abarth
This patch simplifies the SkPicture we generate for Skia. Instead of drawing
everything into a nested SkPicture, we now draw everything into the top-level
picture, which requires us to apply the device scale factor in Dart.