remove getter for imagegenerator factory, update test

include/core/SkImageGenerator.h

Index: include/core/SkImageGenerator.h
diff --git a/include/core/SkImageGenerator.h b/include/core/SkImageGenerator.h
index 46001c85370755ef69e28f2cc9f842268815ddcf..c133476d5b40f8fd3a88a65f5a9ace6dbcb461b5 100644
--- a/include/core/SkImageGenerator.h
+++ b/include/core/SkImageGenerator.h
@@ -221,6 +221,9 @@ protected:
 private:
     const SkImageInfo fInfo;
 
+    // This is our default impl, which may be different on different platforms.
+    // It is called from NewFromEncoded() after it has checked for any runtime factory.
+    // The SkData will never be NULL, as that will have been checked by NewFromEncoded.
     static SkImageGenerator* NewFromEncodedImpl(SkData*);
 };