guard rasterizer and drawlooper setters

Need to land https://codereview.chromium.org/1823513002/ first

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1821533002

Review URL: https://codereview.chromium.org/1821533002
diff --git a/tools/debugger/SkDrawCommand.cpp b/tools/debugger/SkDrawCommand.cpp
index 5941a5d..5bacf02 100644
--- a/tools/debugger/SkDrawCommand.cpp
+++ b/tools/debugger/SkDrawCommand.cpp
@@ -1184,10 +1184,9 @@
                                       SkPaint* target) {
     if (jsonPaint.isMember(SKDEBUGCANVAS_ATTRIBUTE_LOOPER)) {
         Json::Value jsonLooper = jsonPaint[SKDEBUGCANVAS_ATTRIBUTE_LOOPER];
-        SkDrawLooper* looper = (SkDrawLooper*) load_flattenable(jsonLooper, urlDataManager);
+        sk_sp<SkDrawLooper> looper((SkDrawLooper*) load_flattenable(jsonLooper, urlDataManager));
         if (looper != nullptr) {
-            target->setLooper(looper);
-            looper->unref();
+            target->setLooper(std::move(looper));
         }
     }
 }