gm: GMFactory returns a unique_ptr<>

Change-Id: If8a4d3cfdeaef58dd9924af430cfed834519b096
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/232496
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
diff --git a/tools/viewer/Viewer.cpp b/tools/viewer/Viewer.cpp
index 1189703..48e9931 100644
--- a/tools/viewer/Viewer.cpp
+++ b/tools/viewer/Viewer.cpp
@@ -676,7 +676,7 @@
     // GMs
     int firstGM = fSlides.count();
     for (skiagm::GMFactory gmFactory : skiagm::GMRegistry::Range()) {
-        std::unique_ptr<skiagm::GM> gm(gmFactory(nullptr));
+        std::unique_ptr<skiagm::GM> gm(gmFactory());
         if (!CommandLineFlags::ShouldSkip(FLAGS_match, gm->getName())) {
             sk_sp<Slide> slide(new GMSlide(gm.release()));
             fSlides.push_back(std::move(slide));