only pass a real paint to drawPicture if we need to

drawPicture(..., paint)

If paint is non-null, drawPicture will always draw the picture into a
temp layer. Thus we should not blindly pass in a "filtered" paint unless
it will actually draw differently (other than the layer itself).

Side-effect: drawing into a layer is also much slower, so a 2nd reason
to not blindly pass in a non-null paint.

Change-Id: I766c0a129d3bb2882cab976fb2780ef9a09278ee
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/289241
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
2 files changed