NEON Optimized RGBA->PMColor sampling in SkSwizzler

src/codec/SkSwizzler.h

Index: src/codec/SkSwizzler.h
diff --git a/src/codec/SkSwizzler.h b/src/codec/SkSwizzler.h
index 7eebe7f98156506ebd4f45837e2021909fc3b972..1c1c7171d202faf6c79ca4ab39b9fac5bf0ee279 100644
--- a/src/codec/SkSwizzler.h
+++ b/src/codec/SkSwizzler.h
@@ -168,12 +168,29 @@ private:
     static void SkipLeadingGrayAlphaZerosThen(void* dst, const uint8_t* src, int width, int bpp,
                                               int deltaSrc, int offset, const SkPMColor ctable[]);
 
-    // May be NULL.  We have not implemented optimized functions for all supported transforms.
-    const RowProc       fFastProc;
-    // Always non-NULL.  Supports sampling.
+    // Always non-NULL.  Supports all sample sizes.
     const RowProc       fSlowProc;
-    // The actual RowProc we are using.  This depends on if fFastProc is non-NULL and
-    // whether or not we are sampling.
+
+    // Optimized functions are supported for some conversions at various sample sizes.
+    // If a RowProc is NULL, it indicates that the particular conversion at the
+    // particular sample size does not have a fast version.
+    struct FastProcs {
+        FastProcs()
+            : fSampleSize1(nullptr)
+            , fSampleSize2(nullptr)
+            , fSampleSize4(nullptr)
+            , fSampleSize8(nullptr)
+        {}
+
+        RowProc fSampleSize1;
+        RowProc fSampleSize2;
+        RowProc fSampleSize4;
+        RowProc fSampleSize8;
+    };
+    const FastProcs     fFastProcs;
+
+    // The actual RowProc we are using.  This will be equal to one of the fFastProcs
+    // if the appropriate proc is non-NULL.  Otherwise, this will be fSlowProc.
     RowProc             fActualProc;
 
     const SkPMColor*    fColorTable;      // Unowned pointer
@@ -262,7 +279,7 @@ private:
                                           //     fBPP is bitsPerPixel
     const int           fDstBPP;          // Bytes per pixel for the destination color type
 
-    SkSwizzler(RowProc fastProc, RowProc proc, const SkPMColor* ctable, int srcOffset,
+    SkSwizzler(RowProc proc, const FastProcs& fastProcs, const SkPMColor* ctable, int srcOffset,
             int srcWidth, int dstOffset, int dstWidth, int srcBPP, int dstBPP);
 
     int onSetSampleX(int) override;