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/gm/samplerstress.cpp b/gm/samplerstress.cpp
index 10e3cac..ee87f09 100644
--- a/gm/samplerstress.cpp
+++ b/gm/samplerstress.cpp
@@ -76,12 +76,12 @@
     }
 
     void createMaskFilter() {
-        if (fMaskFilter.get()) {
+        if (fMaskFilter) {
             return;
         }
 
         const SkScalar sigma = 1;
-        fMaskFilter.reset(SkBlurMaskFilter::Create(kNormal_SkBlurStyle, sigma));
+        fMaskFilter = SkBlurMaskFilter::Make(kNormal_SkBlurStyle, sigma);
     }
 
     void onDraw(SkCanvas* canvas) override {
@@ -96,7 +96,7 @@
         paint.setAntiAlias(true);
         paint.setTextSize(72);
         paint.setShader(fShader);
-        paint.setMaskFilter(fMaskFilter.get());
+        paint.setMaskFilter(fMaskFilter);
         sk_tool_utils::set_portable_typeface(&paint);
 
         SkRect temp;
@@ -138,7 +138,7 @@
     SkBitmap        fTexture;
     bool            fTextureCreated;
     sk_sp<SkShader> fShader;
-    SkAutoTUnref<SkMaskFilter> fMaskFilter;
+    sk_sp<SkMaskFilter> fMaskFilter;
 
     typedef GM INHERITED;
 };