Refactor 4f gradients using trait templates

src/effects/gradients/Sk4fLinearGradient.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 Sk4fLinearGradient_DEFINED
 #define Sk4fLinearGradient_DEFINED
 
 #include "Sk4fGradientBase.h"
 #include "SkLinearGradient.h"
 
 class SkLinearGradient::
 LinearGradient4fContext final : public GradientShaderBase4fContext {
 public:
     LinearGradient4fContext(const SkLinearGradient&, const ContextRec&);
 
     void shadeSpan(int x, int y, SkPMColor dst[], int count) override;
     void shadeSpan4f(int x, int y, SkPM4f dst[], int count) override;
 
 protected:
     void mapTs(int x, int y, SkScalar ts[], int count) const override;
 
     bool onChooseBlitProcs(const SkImageInfo&, BlitState*) override;
 
 private:
     using INHERITED = GradientShaderBase4fContext;
 
-    template<typename DstType, SkColorProfileType, TileMode>
+    template<DstType, TileMode>
     class LinearIntervalProcessor;
 
-    template <typename DstType, SkColorProfileType, ApplyPremul>
-    void shadePremulSpan(int x, int y, DstType[], int count) const;
+    template <DstType dstType, ApplyPremul premul>
+    void shadePremulSpan(int x, int y, typename DstTraits<dstType, premul>::Type[],
+                         int count) const;
 
-    template <typename DstType, SkColorProfileType, ApplyPremul, SkShader::TileMode tileMode>
-    void shadeSpanInternal(int x, int y, DstType[], int count) const;
+    template <DstType dstType, ApplyPremul premul, SkShader::TileMode tileMode>
+    void shadeSpanInternal(int x, int y, typename DstTraits<dstType, premul>::Type[],
+                           int count) const;
 
     const Interval* findInterval(SkScalar fx) const;
 
     bool isFast() const { return fDstToPosClass == kLinear_MatrixClass; }
 
     static void D32_BlitBW(BlitState*, int x, int y, const SkPixmap& dst, int count);
     static void D64_BlitBW(BlitState*, int x, int y, const SkPixmap& dst, int count);
 
     mutable const Interval*      fCachedInterval;
 };
 
 #endif // Sk4fLinearGradient_DEFINED