Add support for multiple frames in SkCodec

src/codec/SkSwizzler.h

Index: src/codec/SkSwizzler.h
diff --git a/src/codec/SkSwizzler.h b/src/codec/SkSwizzler.h
index a535298a07952886dd3805a2a6571e4c41c1ec93..139ca4fd10123f25fabd35c66403177e39c5362e 100644
--- a/src/codec/SkSwizzler.h
+++ b/src/codec/SkSwizzler.h
@@ -78,6 +78,12 @@ public:
      */
     int swizzleWidth() const { return fSwizzleWidth; }
 
+    /**
+     *  Returns the byte offset at which we write to destination memory, taking
+     *  scaling, subsetting, and partial frames into account.
+     */
+    size_t swizzleOffsetBytes() const { return fDstOffsetBytes; }
+
 private:
 
     /**