Create a scanline decoder without creating a codec

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
 
 #include "SkCodec.h"
 #include "SkImageInfo.h"
 #include "SkJpegDecoderMgr.h"
 #include "SkJpegUtility_codec.h"
 #include "SkStream.h"
 
 extern "C" {
     #include "jpeglib.h"
 }
 
+class SkScanlineDecoder;
+
 /*
  *
  * This class implements the decoding for jpeg images
  *
  */
 class SkJpegCodec : public SkCodec {
 public:
 
     /*
      * Checks the start of the stream to see if the image is a jpeg
      * Does not take ownership of the stream
      */
     static bool IsJpeg(SkStream*);
 
     /*
      * Assumes IsJpeg was called and returned true
      * Creates a jpeg decoder
      * Takes ownership of the stream
      */
     static SkCodec* NewFromStream(SkStream*);
 
+    /*
+     * Assumes IsJpeg was called and returned true
+     * Creates a jpeg scanline decoder
+     * Takes ownership of the stream
+     */
+    static SkScanlineDecoder* NewSDFromStream(SkStream*);
+
 protected:
 
     /*
      * Recommend a set of destination dimensions given a requested scale
      */
     SkISize onGetScaledDimensions(float desiredScale) const override;
 
     /*
      * Initiates the jpeg decode
      */
     Result onGetPixels(const SkImageInfo& dstInfo, void* dst, size_t dstRowBytes, const Options&,
             SkPMColor*, int*) override;
 
     SkEncodedFormat onGetEncodedFormat() const override {
         return kJPEG_SkEncodedFormat;
     }
 
-    SkScanlineDecoder* onGetScanlineDecoder(const SkImageInfo& dstInfo, const Options& options,
-            SkPMColor ctable[], int* ctableCount) override;
-
 private:
 
     /*
      * Read enough of the stream to initialize the SkJpegCodec.
      * Returns a bool representing success or failure.
      *
      * @param codecOut
      * If this returns true, and codecOut was not NULL,
      * codecOut will be set to a new SkJpegCodec.
      *
@@ skipping 47 matching lines @@
             const Options& options);
 
     SkAutoTDelete<JpegDecoderMgr> fDecoderMgr;
 
     friend class SkJpegScanlineDecoder;
 
     typedef SkCodec INHERITED;
 };
 
 #endif