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..203d692cf33c41ceeaf178f64e06969f434af6d7 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 +20,25 @@ public:
     class LinearGradientContext : public SkGradientShaderBase::GradientShaderBaseContext {
     public:
         LinearGradientContext(const SkLinearGradient&, const ContextRec&);
-        ~LinearGradientContext() {}
 
         void shadeSpan(int x, int y, SkPMColor dstC[], int count) override;
         void shadeSpan16(int x, int y, uint16_t dstC[], int count) override;
 
+        struct Rec {
+            Sk4f    fColor;
+            float   fPos;
+            float   fPosScale;
+        };
     private:
+        SkTDArray<Rec>  fRecs;
+        bool            fApplyAlphaAfterInterp;
+
+        void shade4_clamp(int x, int y, SkPMColor dstC[], int count);
+        template <bool> void shade4_pos_clamp(SkPMColor dstC[], int count, float fx, float dx,
+                                              float invDx, Sk4f dither0, Sk4f dither1);
+        template <bool> void shade4_neg_clamp(SkPMColor dstC[], int count, float fx, float dx,
+                                              float invDx, Sk4f dither0, Sk4f dither1);
+
         typedef SkGradientShaderBase::GradientShaderBaseContext INHERITED;
     };