Outline SkImageFilter Make methods

include/effects/SkComposeImageFilter.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkComposeImageFilter_DEFINED
 #define SkComposeImageFilter_DEFINED
 
 #include "SkImageFilter.h"
 
 class SK_API SkComposeImageFilter : public SkImageFilter {
 public:
-    static sk_sp<SkImageFilter> Make(sk_sp<SkImageFilter> outer, sk_sp<SkImageFilter> inner) {
-        if (!outer) {
-            return inner;
-        }
-        if (!inner) {
-            return outer;
-        }
-        sk_sp<SkImageFilter> inputs[2] = { std::move(outer), std::move(inner) };
-        return sk_sp<SkImageFilter>(new SkComposeImageFilter(inputs));
-    }
+    static sk_sp<SkImageFilter> Make(sk_sp<SkImageFilter> outer, sk_sp<SkImageFilter> inner);
+
     SkRect computeFastBounds(const SkRect& src) const override;
 
     SK_TO_STRING_OVERRIDE()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkComposeImageFilter)
 
 #ifdef SK_SUPPORT_LEGACY_IMAGEFILTER_PTR
     static SkImageFilter* Create(SkImageFilter* outer, SkImageFilter* inner) {
         return Make(sk_ref_sp<SkImageFilter>(outer),
                     sk_ref_sp<SkImageFilter>(inner)).release();
     }
 #endif
 
 protected:
     explicit SkComposeImageFilter(sk_sp<SkImageFilter> inputs[2]) : INHERITED(inputs, 2, nullptr) {
         SkASSERT(inputs[0].get());
         SkASSERT(inputs[1].get());
     }
     sk_sp<SkSpecialImage> onFilterImage(SkSpecialImage* source, const Context&,
                                         SkIPoint* offset) const override;
     SkIRect onFilterBounds(const SkIRect&, const SkMatrix&, MapDirection) const override;
 
 private:
     typedef SkImageFilter INHERITED;
 };
 
 #endif