switch maskfilters to sk_sp

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1852113003

Review URL: https://codereview.chromium.org/1852113003
diff --git a/samplecode/SampleTextAlpha.cpp b/samplecode/SampleTextAlpha.cpp
index a57c016..cb07e92 100644
--- a/samplecode/SampleTextAlpha.cpp
+++ b/samplecode/SampleTextAlpha.cpp
@@ -52,9 +52,8 @@
 
         paint.setARGB(fByte, 0xFF, 0xFF, 0xFF);
 
-        paint.setMaskFilter(SkBlurMaskFilter::Create(kNormal_SkBlurStyle,
-                                    SkBlurMask::ConvertRadiusToSigma(SkIntToScalar(3))));
-        paint.getMaskFilter()->unref();
+        paint.setMaskFilter(SkBlurMaskFilter::Make(kNormal_SkBlurStyle,
+                                                   SkBlurMask::ConvertRadiusToSigma(3)));
 
         SkRandom rand;