Update MagnifierImageFilter to sk_sp

TBR=reed@google.com

GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1864843002

Review URL: https://codereview.chromium.org/1864843002
diff --git a/gm/imagemagnifier.cpp b/gm/imagemagnifier.cpp
index 7363981..5697aa2 100644
--- a/gm/imagemagnifier.cpp
+++ b/gm/imagemagnifier.cpp
@@ -15,11 +15,11 @@
 DEF_SIMPLE_GM_BG(imagemagnifier, canvas, WIDTH, HEIGHT, SK_ColorBLACK) {
         SkPaint filterPaint;
         filterPaint.setImageFilter(
-            SkMagnifierImageFilter::Create(
+            SkMagnifierImageFilter::Make(
                 SkRect::MakeXYWH(SkIntToScalar(100), SkIntToScalar(100),
                                  SkIntToScalar(WIDTH / 2),
                                  SkIntToScalar(HEIGHT / 2)),
-                100))->unref();
+                100, nullptr));
         canvas->saveLayer(nullptr, &filterPaint);
         const char* str = "The quick brown fox jumped over the lazy dog.";
         SkRandom rand;