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/gm/gm.h b/gm/gm.h
index c799532..8536709 100644
--- a/gm/gm.h
+++ b/gm/gm.h
@@ -119,7 +119,8 @@
         bool     fHaveCalledOnceBeforeDraw;
     };
 
-    typedef sk_tools::Registry<GM*(*)(void*)> GMRegistry;
+    typedef GM*(*GMFactory)(void*) ;
+    typedef sk_tools::Registry<GMFactory> GMRegistry;
 
     class SimpleGM : public skiagm::GM {
     public: