Create a scanline decoder without creating a codec

src/codec/SkJpegCodec.h

Index: src/codec/SkJpegCodec.h
diff --git a/src/codec/SkJpegCodec.h b/src/codec/SkJpegCodec.h
index 1844269e6b3eff13a2e53dd636a8845e299c8739..5e2135cdffb71b66faa6a2c1cb24ae895626d31d 100644
--- a/src/codec/SkJpegCodec.h
+++ b/src/codec/SkJpegCodec.h
@@ -18,6 +18,8 @@ extern "C" {
     #include "jpeglib.h"
 }
 
+class SkScanlineDecoder;
+
 /*
  *
  * This class implements the decoding for jpeg images
@@ -39,6 +41,13 @@ public:
      */
     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:
 
     /*
@@ -56,9 +65,6 @@ protected:
         return kJPEG_SkEncodedFormat;
     }
 
-    SkScanlineDecoder* onGetScanlineDecoder(const SkImageInfo& dstInfo, const Options& options,
-            SkPMColor ctable[], int* ctableCount) override;
-
 private:
 
     /*