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/bench/BlurRoundRectBench.cpp b/bench/BlurRoundRectBench.cpp
index 5213276..85852d5 100644
--- a/bench/BlurRoundRectBench.cpp
+++ b/bench/BlurRoundRectBench.cpp
@@ -67,7 +67,7 @@
         dullPaint.setAntiAlias(true);
 
         SkPaint loopedPaint;
-        loopedPaint.setLooper(looperBuilder.detachLooper())->unref();
+        loopedPaint.setLooper(looperBuilder.detach());
         loopedPaint.setAntiAlias(true);
         loopedPaint.setColor(SK_ColorCYAN);