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..4c7e4b33991e44ba1ff19107437ed32fa4ac80bc 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().
      */
@@ -221,10 +221,11 @@ protected:
     // V15: Remove A1 bitmpa config (and renumber remaining configs)
     // V16: Move SkPath's isOval flag to SkPathRef
     // V17: SkPixelRef now writes SkImageInfo
+    // V18: SkBitmap now records x,y for its pixelref origin, instead of offset.
 #ifndef DELETE_THIS_CODE_WHEN_SKPS_ARE_REBUILT_AT_V16_AND_ALL_OTHER_INSTANCES_TOO
     static const uint32_t PRIOR_PICTURE_VERSION = 15;  // TODO: remove when .skps regenerated
 #endif
-    static const uint32_t PICTURE_VERSION = 17;
+    static const uint32_t PICTURE_VERSION = 18;
 
     // fPlayback, fRecord, fWidth & fHeight are protected to allow derived classes to
     // install their own SkPicturePlayback-derived players,SkPictureRecord-derived