sk_tool::Registry: make an iterator.

Change-Id: Icf4e31b50bbd91b7ea330a1300f736d6dfd0a41c
Reviewed-on: https://skia-review.googlesource.com/144500
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
Auto-Submit: Hal Canary <halcanary@google.com>
diff --git a/dm/DMSrcSink.h b/dm/DMSrcSink.h
index 257ca8b..a97b077 100644
--- a/dm/DMSrcSink.h
+++ b/dm/DMSrcSink.h
@@ -100,7 +100,7 @@
 
 class GMSrc : public Src {
 public:
-    explicit GMSrc(skiagm::GMRegistry::Factory);
+    explicit GMSrc(skiagm::GMFactory);
 
     Error draw(SkCanvas*) const override;
     SkISize size() const override;
@@ -108,7 +108,7 @@
     void modifyGrContextOptions(GrContextOptions* options) const override;
 
 private:
-    skiagm::GMRegistry::Factory fFactory;
+    skiagm::GMFactory fFactory;
 };
 
 class CodecSrc : public Src {