Implement multi-color-stops in linear gradients using Sk4f

src/effects/gradients/SkLinearGradient.h

Index: src/effects/gradients/SkLinearGradient.h
diff --git a/src/effects/gradients/SkLinearGradient.h b/src/effects/gradients/SkLinearGradient.h
index 488775ea9330dd35e2a6b30ebb2a377829ffa18d..34bafa60ec60441a9753c52622b6bc107d4514a5 100644
--- a/src/effects/gradients/SkLinearGradient.h
+++ b/src/effects/gradients/SkLinearGradient.h
@@ -9,6 +9,7 @@
 #define SkLinearGradient_DEFINED
 
 #include "SkGradientShaderPriv.h"
+#include "SkNx.h"
 
 class SkLinearGradient : public SkGradientShaderBase {
 public:
@@ -19,12 +20,18 @@ public:
     class LinearGradientContext : public SkGradientShaderBase::GradientShaderBaseContext {
     public:
         LinearGradientContext(const SkLinearGradient&, const ContextRec&);
-        ~LinearGradientContext() {}
+        ~LinearGradientContext() override;
 
         void shadeSpan(int x, int y, SkPMColor dstC[], int count) override;
         void shadeSpan16(int x, int y, uint16_t dstC[], int count) override;
 
     private:
+        Sk4f*   fColors4;
+        float*  fPos;
+        float*  fPosScale;
+        int fColorCount;
+        void shadeSpan4(int x, int y, SkPMColor dstC[], int count);
+
         typedef SkGradientShaderBase::GradientShaderBaseContext INHERITED;
     };