Add convert-to-nia command-line program

Together with similar programs in other repositories, this helps find
disagreements between Chromium's, Skia's and Wuffs' image decoders.

Change-Id: I9a0d8aabb47b1d5bd29f9139755e76bf56ab4bbe
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/290618
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 333995d..f3364d8 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1717,6 +1717,10 @@
     }
   }
   if (target_cpu != "wasm") {
+    test_app("convert-to-nia") {
+      sources = [ "tools/convert-to-nia.cpp" ]
+      deps = [ ":skia" ]
+    }
     test_app("imgcvt") {
       sources = [ "tools/imgcvt.cpp" ]
       deps = [