Fix DM blaze build (PNG output is now dependent on picture_utils)

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1902333002

Review URL: https://codereview.chromium.org/1902333002
diff --git a/public.bzl b/public.bzl
index aea55c6..ef99c9f 100644
--- a/public.bzl
+++ b/public.bzl
@@ -408,6 +408,7 @@
         "tools/flags/*.h",
         "tools/gpu/**/*.cpp",
         "tools/gpu/**/*.h",
+        "tools/picture_utils.cpp",
         "tools/random_parse_path.cpp",
         "tools/random_parse_path.h",
         "tools/sk_tool_utils.cpp",