change offset to xy for pixelref subsetting

src/image/SkSurface_Raster.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 "SkSurface_Base.h"
 #include "SkImagePriv.h"
 #include "SkCanvas.h"
@@ skipping 105 matching lines @@
 SkImage* SkSurface_Raster::onNewImageSnapshot() {
     return SkNewImageFromBitmap(fBitmap, fWeOwnThePixels);
 }
 
 void SkSurface_Raster::onCopyOnWrite(ContentChangeMode mode) {
     // are we sharing pixelrefs with the image?
     SkASSERT(NULL != this->getCachedImage());
     if (SkBitmapImageGetPixelRef(this->getCachedImage()) == fBitmap.pixelRef()) {
         SkASSERT(fWeOwnThePixels);
         if (kDiscard_ContentChangeMode == mode) {
-            fBitmap.setPixelRef(NULL, 0);
+            fBitmap.setPixelRef(NULL);
             fBitmap.allocPixels();
         } else {
             SkBitmap prev(fBitmap);
             prev.deepCopyTo(&fBitmap, prev.config());
         }
         // Now fBitmap is a deep copy of itself (and therefore different from
         // what is being used by the image. Next we update the canvas to use
         // this as its backend, so we can't modify the image's pixels anymore.
         SkASSERT(NULL != this->getCachedCanvas());
         this->getCachedCanvas()->getDevice()->replaceBitmapBackendForRasterSurface(fBitmap);
@@ skipping 17 matching lines @@
     if (!SkSurface_Raster::Valid(info)) {
         return NULL;
     }
 
     SkAutoTUnref<SkPixelRef> pr(SkMallocPixelRef::NewAllocate(info, 0, NULL));
     if (NULL == pr.get()) {
         return NULL;
     }
     return SkNEW_ARGS(SkSurface_Raster, (info, pr, info.minRowBytes()));
 }