switch surface to sk_sp

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1817383002
CQ_EXTRA_TRYBOTS=client.skia.compile:Build-Ubuntu-GCC-x86_64-Release-CMake-Trybot,Build-Mac-Clang-x86_64-Release-CMake-Trybot

Review URL: https://codereview.chromium.org/1817383002
diff --git a/gm/imagesource2.cpp b/gm/imagesource2.cpp
index 46c42f1..db8a9f6 100644
--- a/gm/imagesource2.cpp
+++ b/gm/imagesource2.cpp
@@ -41,7 +41,7 @@
             SK_ColorWHITE,   SK_ColorGRAY,
         };
 
-        SkAutoTUnref<SkSurface> surface(SkSurface::NewRasterN32Premul(kImageSize, kImageSize));
+        auto surface(SkSurface::MakeRasterN32Premul(kImageSize, kImageSize));
         SkCanvas* canvas = surface->getCanvas();
 
         int curColor = 0;