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/mipmap.cpp b/gm/mipmap.cpp
index 4b1912a..9a0f060 100644
--- a/gm/mipmap.cpp
+++ b/gm/mipmap.cpp
@@ -13,7 +13,7 @@
 
 static sk_sp<SkImage> make_image() {
     const SkImageInfo info = SkImageInfo::MakeN32Premul(319, 52);
-    SkAutoTUnref<SkSurface> surface(SkSurface::NewRaster(info));
+    auto surface(SkSurface::MakeRaster(info));
     SkCanvas* canvas = surface->getCanvas();
     canvas->drawColor(sk_tool_utils::color_to_565(0xFFF8F8F8));