switch surface to sk_sp

gm/verylargebitmap.cpp

Index: gm/verylargebitmap.cpp
diff --git a/gm/verylargebitmap.cpp b/gm/verylargebitmap.cpp
index b3ed5603a61dafe893ce4d953457053885823989..78f8f59c8aa92d9b5c5b855375cdfe9d7d12441e 100644
--- a/gm/verylargebitmap.cpp
+++ b/gm/verylargebitmap.cpp
@@ -23,7 +23,7 @@ static void draw(SkCanvas* canvas, int width, int height, SkColor colors[2]) {
 }
 
 static sk_sp<SkImage> make_raster_image(int width, int height, SkColor colors[2]) {
-    SkAutoTUnref<SkSurface> surface(SkSurface::NewRasterN32Premul(width, height));
+    auto surface(SkSurface::MakeRasterN32Premul(width, height));
     draw(surface->getCanvas(), width, height, colors);
     return surface->makeImageSnapshot();
 }