flag to use const& instead of const* for src-rect

gm/mipmap.cpp

Index: gm/mipmap.cpp
diff --git a/gm/mipmap.cpp b/gm/mipmap.cpp
index 6163a3ac5169dc75e1f9ccca6f7ab20c7d982808..596cc19d6e53bf3dee3259412016452cab460b62 100644
--- a/gm/mipmap.cpp
+++ b/gm/mipmap.cpp
@@ -42,7 +42,7 @@ static void test_mip(SkCanvas* canvas) {
     canvas->translate(20, 20);
     for (int i = 0; i < 4; ++i) {
         paint.setFilterQuality(SkFilterQuality(i));
-        canvas->drawImageRect(img, NULL, dst, &paint);
+        canvas->drawImageRect(img, dst, &paint);
         canvas->translate(0, 20);
     }
     canvas->drawImage(img, 20, 20, NULL);