Use possible read_partial_scanlines() API in SkJpegCodec

src/codec/SkJpegCodec.h

Index: src/codec/SkJpegCodec.h
diff --git a/src/codec/SkJpegCodec.h b/src/codec/SkJpegCodec.h
index 8e2db81b73a1ff8f1a6b6a6407721d44ce089313..9254dcc1fbf8b44345d46ec1372463b087c878b6 100644
--- a/src/codec/SkJpegCodec.h
+++ b/src/codec/SkJpegCodec.h
@@ -114,6 +114,10 @@ private:
     // scanline decoding
     SkAutoTMalloc<uint8_t>     fStorage;    // Only used if sampling is needed
     uint8_t*                   fSrcRow;     // Only used if sampling is needed
+    // libjpeg-turbo provides some subsetting.  In the case that libjpeg-turbo
+    // cannot take the exact the subset that we need, we will use the swizzler
+    // to further subset the output from libjpeg-turbo.
+    SkIRect                    fSwizzlerSubset;
     SkAutoTDelete<SkSwizzler>  fSwizzler;
     
     typedef SkCodec INHERITED;