Outline SkImageFilter Make methods

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
 
 #include "SkImageFilter.h"
 #include "SkPoint.h"
 
 // Fun mode that scales down (only) and then scales back up to look pixelated
 class SK_API SkDownSampleImageFilter : public SkImageFilter {
 public:
-    static sk_sp<SkImageFilter> Make(SkScalar scale, sk_sp<SkImageFilter> input) {
-        if (!SkScalarIsFinite(scale)) {
-            return nullptr;
-        }
-        // we don't support scale in this range
-        if (scale > SK_Scalar1 || scale <= 0) {
-            return nullptr;
-        }
-        return sk_sp<SkImageFilter>(new SkDownSampleImageFilter(scale, std::move(input)));
-    }
+    static sk_sp<SkImageFilter> Make(SkScalar scale, sk_sp<SkImageFilter> input);
 
     SK_TO_STRING_OVERRIDE()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkDownSampleImageFilter)
 
 #ifdef SK_SUPPORT_LEGACY_IMAGEFILTER_PTR
     static SkImageFilter* Create(SkScalar scale, SkImageFilter* input = nullptr) {
         return Make(scale, sk_ref_sp<SkImageFilter>(input)).release();
     }
 #endif
 
 protected:
     void flatten(SkWriteBuffer&) const override;
 
     sk_sp<SkSpecialImage> onFilterImage(SkSpecialImage* source, const Context&,
                                         SkIPoint* offset) const override;
 
 private:
     SkDownSampleImageFilter(SkScalar scale, sk_sp<SkImageFilter> input)
         : INHERITED(&input, 1, nullptr), fScale(scale) {}
 
     SkScalar fScale;
 
     typedef SkImageFilter INHERITED;
 };
 
 #endif