Switch SkDownSampleImageFilter over to new onFilterImage interface

include/effects/SkTestImageFilters.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef _SkTestImageFilters_h
 #define _SkTestImageFilters_h
 
@@ skipping 12 matching lines @@
             return NULL;
         }
         return new SkDownSampleImageFilter(scale, input);
     }
 
     SK_TO_STRING_OVERRIDE()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkDownSampleImageFilter)
 
 protected:
     void flatten(SkWriteBuffer&) const override;
-    bool onFilterImageDeprecated(Proxy*, const SkBitmap& src, const Context&, SkBitmap* result,
-                                 SkIPoint* loc) const override;
+
+    sk_sp<SkSpecialImage> onFilterImage(SkSpecialImage* source, const Context&,
+                                        SkIPoint* offset) const override;
 
 private:
     SkDownSampleImageFilter(SkScalar scale, SkImageFilter* input)
         : INHERITED(1, &input), fScale(scale) {}
 
     SkScalar fScale;
 
     typedef SkImageFilter INHERITED;
 };
 
 #endif