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/src/image/SkSurface_Gpu.h b/src/image/SkSurface_Gpu.h
index 72e9caf..1e76f26 100644
--- a/src/image/SkSurface_Gpu.h
+++ b/src/image/SkSurface_Gpu.h
@@ -22,8 +22,8 @@
     GrBackendObject onGetTextureHandle(BackendHandleAccess) override;
     bool onGetRenderTargetHandle(GrBackendObject*, BackendHandleAccess) override;
     SkCanvas* onNewCanvas() override;
-    SkSurface* onNewSurface(const SkImageInfo&) override;
-    SkImage* onNewImageSnapshot(SkBudgeted, ForceCopyMode) override;
+    sk_sp<SkSurface> onNewSurface(const SkImageInfo&) override;
+    sk_sp<SkImage> onNewImageSnapshot(SkBudgeted, ForceCopyMode) override;
     void onCopyOnWrite(ContentChangeMode) override;
     void onDiscard() override;
     void onPrepareForExternalIO() override;