Add subsetting to SkScanlineDecoder

src/codec/SkJpegCodec.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 SkJpegCodec_DEFINED
 #define SkJpegCodec_DEFINED
 
@@ skipping 85 matching lines @@
     SkJpegCodec(const SkImageInfo& srcInfo, SkStream* stream, JpegDecoderMgr* decoderMgr);
 
     /*
      * Checks if the conversion between the input image and the requested output
      * image has been implemented
      * Sets the output color space
      */
     bool setOutputColorSpace(const SkImageInfo& dst);
 
     // scanline decoding
+    void initializeSwizzler(const SkImageInfo& dstInfo, const Options& options);
     SkSampler* getSampler(bool createIfNecessary) override;
     Result onStartScanlineDecode(const SkImageInfo& dstInfo, const Options& options,
-                   SkPMColor ctable[], int* ctableCount) override;
+            SkPMColor ctable[], int* ctableCount) override;
     int onGetScanlines(void* dst, int count, size_t rowBytes) override;
     bool onSkipScanlines(int count) override;
 
     SkAutoTDelete<JpegDecoderMgr> fDecoderMgr;
     // We will save the state of the decompress struct after reading the header.
     // This allows us to safely call onGetScaledDimensions() at any time.
     const int                     fReadyState;
 
     // scanline decoding
     SkAutoMalloc               fStorage;    // Only used if sampling is needed
     uint8_t*                   fSrcRow;     // Only used if sampling is needed
     SkAutoTDelete<SkSwizzler>  fSwizzler;
     
     typedef SkCodec INHERITED;
 };
 
 #endif