Fix SkSwizzler bug

src/codec/SkMaskSwizzler.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #ifndef SkMaskSwizzler_DEFINED
 #define SkMaskSwizzler_DEFINED
 
 #include "SkMasks.h"
@@ skipping 35 matching lines @@
     }
 
 private:
 
     /*
      * Row procedure used for swizzle
      */
     typedef SkSwizzler::ResultAlpha (*RowProc)(void* dstRow, const uint8_t* srcRow, int width,
             SkMasks* masks, uint32_t startX, uint32_t sampleX);
 
-    SkMaskSwizzler(SkMasks* masks, RowProc proc, int srcWidth, int srcOffset);
+    SkMaskSwizzler(SkMasks* masks, RowProc proc, int subsetWidth, int srcOffset);
 
     int onSetSampleX(int) override;
 
     SkMasks*        fMasks;           // unowned
     const RowProc   fRowProc;
 
     // FIXME: Can this class share more with SkSwizzler? These variables are all the same.
-    const int       fSrcWidth;        // Width of the source - i.e. before any sampling.
+    const int       fSubsetWidth;     // Width of the subset of source before any sampling.
     int             fDstWidth;        // Width of dst, which may differ with sampling.
     int             fSampleX;
     int             fSrcOffset;
     int             fX0;
 };
 
 #endif