Add subsetting to 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 871cbacb04c67ecc4e87f1e2da850be1acd477af..1d51f870788cc2ea7397bea47ad9c741bfc23f61 100644
--- a/src/codec/SkCodec_libgif.h
+++ b/src/codec/SkCodec_libgif.h
@@ -130,8 +130,11 @@ private:
      *                 adjusted if the image frame size does not match the size
      *                 indicated in the header.
      * @param zeroInit Indicates if destination memory is zero initialized.
+     * @param subsetLeft Left offset for each row decode.
+     * @param subsetWidth Width of each row decode.
      */
-    Result initializeSwizzler(const SkImageInfo& dstInfo, ZeroInitialized zeroInit);
+    Result initializeSwizzler(const SkImageInfo& dstInfo,
+            ZeroInitialized zeroInit, int subsetLeft, int subsetWidth);
 
     SkSampler* getSampler(bool createIfNecessary) override { return fSwizzler; }
 
@@ -141,7 +144,8 @@ private:
     bool readRow();
 
     Result onStartScanlineDecode(const SkImageInfo& dstInfo, const Options& opts,
-                   SkPMColor inputColorPtr[], int* inputColorCount) override;
+                   SkPMColor inputColorPtr[], int* inputColorCount, int subsetLeft,
+                   int subsetWidth) override;
 
     int onGetScanlines(void* dst, int count, size_t rowBytes) override;