change offset to xy for pixelref subsetting

tests/PictureTest.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Test.h"
 #include "TestClassDef.h"
 #include "SkBitmapDevice.h"
@@ skipping 322 matching lines @@
     SkPicture picture;
     SkCanvas* recordingCanvas = picture.beginRecording(100, 100);
     recordingCanvas->drawBitmap(bm, 0, 0);
     picture.endRecording();
 
     SkCanvas canvas;
     canvas.drawPicture(picture);
 }
 #endif
 
-static SkData* encode_bitmap_to_data(size_t* offset, const SkBitmap& bm) {
-    *offset = 0;
+static SkData* encode_bitmap_to_data(size_t*, const SkBitmap& bm) {
     return SkImageEncoder::EncodeData(bm, SkImageEncoder::kPNG_Type, 100);
 }
 
 static SkData* serialized_picture_from_bitmap(const SkBitmap& bitmap) {
     SkPicture picture;
     SkCanvas* canvas = picture.beginRecording(bitmap.width(), bitmap.height());
     canvas->drawBitmap(bitmap, 0, 0);
     SkDynamicMemoryWStream wStream;
     picture.serialize(&wStream, &encode_bitmap_to_data);
     return wStream.copyToData();
@@ skipping 278 matching lines @@
     test_bad_bitmap();
 #endif
     test_peephole();
     test_gatherpixelrefs(reporter);
     test_bitmap_with_encoded_data(reporter);
     test_clone_empty(reporter);
     test_clip_bound_opt(reporter);
     test_clip_expansion(reporter);
     test_hierarchical(reporter);
 }