change offset to xy for pixelref subsetting

include/core/SkPicture.h

Index: include/core/SkPicture.h
diff --git a/include/core/SkPicture.h b/include/core/SkPicture.h
index a1d7644e53570c991c376747b56b1d14a72ffcfe..39691aec57c27388088c0308c192cb76cf3af1a9 100644
--- a/include/core/SkPicture.h
+++ b/include/core/SkPicture.h
@@ -172,8 +172,8 @@ public:
      *  signature can be passed to serialize() and SkOrderedWriteBuffer.
      *  Returning NULL will tell the SkOrderedWriteBuffer to use
      *  SkBitmap::flatten() to store the bitmap.
-     *  @param pixelRefOffset Output parameter, telling the deserializer what
-     *      offset in the bm's pixelRef corresponds to the encoded data.
+     *
+     *  @param pixelRefOffset DEPRECATED -- caller assumes it will return 0.
      *  @return SkData If non-NULL, holds encoded data representing the passed
      *      in bitmap. The caller is responsible for calling unref().
      */