Add a --scale flag to skpbench

Change-Id: Idd7698b59e09bdcc688ae3601d9ec343c37592d8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/264881
Reviewed-by: Nathaniel Nifong <nifong@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
1 file changed