Update SkAlphaThresholdFilter to sk_sp

gm/imagealphathreshold.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "gm.h"
 #include "SkAlphaThresholdFilter.h"
 #include "SkRandom.h"
@@ skipping 17 matching lines @@
 }
 
 SkPaint create_filter_paint() {
     SkIRect rects[2];
     rects[0] = SkIRect::MakeXYWH(0, 150, WIDTH, HEIGHT - 300);
     rects[1] = SkIRect::MakeXYWH(150, 0, WIDTH - 300, HEIGHT);
     SkRegion region;
     region.setRects(rects, 2);
 
     SkPaint paint;
-    paint.setImageFilter(SkAlphaThresholdFilter::Create(region, 0.2f, 0.7f))->unref();
+    paint.setImageFilter(SkAlphaThresholdFilter::Make(region, 0.2f, 0.7f, nullptr));
     return paint;
 }
 
 };
 
 namespace skiagm {
 
 class ImageAlphaThresholdGM : public GM {
 public:
     ImageAlphaThresholdGM() {
@@ skipping 61 matching lines @@
 private:
     typedef GM INHERITED;
 };
 
 //////////////////////////////////////////////////////////////////////////////
 
 DEF_GM(return new ImageAlphaThresholdGM();)
 DEF_GM(return new ImageAlphaThresholdSurfaceGM();)
 
 }