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

src/effects/SkPictureImageFilter.cpp

 /*
  * Copyright 2013 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 "SkPictureImageFilter.h"
 #include "SkDevice.h"
 #include "SkCanvas.h"
@@ skipping 53 matching lines @@
     }
 
     SkCanvas canvas(device.get());
     SkPaint paint;
 
     canvas.translate(-SkIntToScalar(bounds.fLeft), -SkIntToScalar(bounds.fTop));
     canvas.concat(matrix);
     canvas.drawPicture(*fPicture);
 
     *result = device.get()->accessBitmap(false);
-    offset->fX += bounds.fLeft;
-    offset->fY += bounds.fTop;
+    offset->fX = bounds.fLeft;
+    offset->fY = bounds.fTop;
     return true;
 }