update dox for drawPaint

Bug: skia:7745
Change-Id: I3b43aa28349d8525f85f6caaf416659f90c9b285
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/328816
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
1 file changed