Bring sk_sp to GrDrawContext

This is split out of: https://codereview.chromium.org/1914883002/ (Refactor drawContext/RenderTarget creation)

GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1918003003

Review-Url: https://codereview.chromium.org/1918003003
diff --git a/src/gpu/GrLayerCache.cpp b/src/gpu/GrLayerCache.cpp
index 3c7ab88..8bdc3fb 100644
--- a/src/gpu/GrLayerCache.cpp
+++ b/src/gpu/GrLayerCache.cpp
@@ -468,8 +468,8 @@
     SkASSERT(0 == fPictureHash.count());
 
     if (fAtlas->getTextureOrNull()) {
-        SkAutoTUnref<GrDrawContext> drawContext(
-                                    fContext->drawContext(fAtlas->getTexture()->asRenderTarget()));
+        sk_sp<GrDrawContext> drawContext(
+                       fContext->drawContext(sk_ref_sp(fAtlas->getTexture()->asRenderTarget())));
 
         if (drawContext) {
             drawContext->discard();