experimental/xps_to_png: pass in DPI as program argument NOTRY=true Change-Id: Ieb4f43c69a4f185d8e7877c9c736bd6a7d7b1eac Reviewed-on: https://skia-review.googlesource.com/4761 Reviewed-by: Hal Canary <halcanary@google.com> Commit-Queue: Hal Canary <halcanary@google.com>