Make SkImageFilter crop rects relative to the primitive origin, instead of relative to their parent

src/effects/SkBitmapSource.cpp

 /*
  * Copyright 2012 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmapSource.h"
 #include "SkDevice.h"
 #include "SkCanvas.h"
@@ skipping 55 matching lines @@
     dstRect.offset(-SkIntToScalar(dstIRect.fLeft), -SkIntToScalar(dstIRect.fTop));
     paint.setXfermodeMode(SkXfermode::kSrc_Mode);
     // FIXME: this probably shouldn't be necessary, but drawBitmapRectToRect asserts
     // None filtering when it's translate-only
     paint.setFilterLevel(
         fSrcRect.width() == dstRect.width() && fSrcRect.height() == dstRect.height() ?
         SkPaint::kNone_FilterLevel : SkPaint::kMedium_FilterLevel);
     canvas.drawBitmapRectToRect(fBitmap, &fSrcRect, dstRect, &paint);
 
     *result = device.get()->accessBitmap(false);
-    offset->fX += dstIRect.fLeft;
-    offset->fY += dstIRect.fTop;
+    offset->fX = dstIRect.fLeft;
+    offset->fY = dstIRect.fTop;
     return true;
 }