Move all knowledge of X sampling into SkScaledCodec

src/codec/SkCodec_libgif.h

Index: src/codec/SkCodec_libgif.h
diff --git a/src/codec/SkCodec_libgif.h b/src/codec/SkCodec_libgif.h
index d7dc2b9e1d401242d2c730f805a947b75ca31de0..c29cbdb9d588acf27ee614bda1acd30fdd6693b2 100644
--- a/src/codec/SkCodec_libgif.h
+++ b/src/codec/SkCodec_libgif.h
@@ -124,6 +124,8 @@ private:
      */
     Result initializeSwizzler(const SkImageInfo& dstInfo, ZeroInitialized zeroInit);
 
+    SkSampler* getSampler() override { return fSwizzler; }
+
     /*
      * @return kSuccess if the read is successful and kIncompleteInput if the
      *         read fails.