Switch new SkImageFilter internal methods over to sk_sp

include/effects/SkPaintImageFilter.h

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkPaintImageFilter_DEFINED
 #define SkPaintImageFilter_DEFINED
 
@@ skipping 13 matching lines @@
      */
     static SkImageFilter* Create(const SkPaint& paint, const CropRect* rect = NULL);
 
     bool canComputeFastBounds() const override;
 
     SK_TO_STRING_OVERRIDE()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkPaintImageFilter)
 
 protected:
     void flatten(SkWriteBuffer&) const override;
-    SkSpecialImage* onFilterImage(SkSpecialImage* source, const Context&,
-                                  SkIPoint* offset) const override;
+    sk_sp<SkSpecialImage> onFilterImage(SkSpecialImage* source, const Context&,
+                                        SkIPoint* offset) const override;
 
 private:
     SkPaintImageFilter(const SkPaint& paint, const CropRect* rect);
 
     SkPaint fPaint;
 
     typedef SkImageFilter INHERITED;
 };
 
 #endif