Add getYUV8Planes() API to SkCodec

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1549473003

Review URL: https://codereview.chromium.org/1549473003
diff --git a/src/codec/SkJpegCodec.h b/src/codec/SkJpegCodec.h
index 8e2db81..283dd8f 100644
--- a/src/codec/SkJpegCodec.h
+++ b/src/codec/SkJpegCodec.h
@@ -48,6 +48,10 @@
     Result onGetPixels(const SkImageInfo& dstInfo, void* dst, size_t dstRowBytes, const Options&,
             SkPMColor*, int*, int*) override;
 
+    bool onQueryYUV8(YUVSizeInfo* sizeInfo, SkYUVColorSpace* colorSpace) const override;
+
+    Result onGetYUV8Planes(const YUVSizeInfo& sizeInfo, void* pixels[3]) override;
+
     SkEncodedFormat onGetEncodedFormat() const override {
         return kJPEG_SkEncodedFormat;
     }