SkImage_Raster's pixels are always immutable.

tests/SkImageTest.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCanvas.h"
 #include "SkImagePriv.h"
 #include "Test.h"
 
 static const int gWidth = 20;
 static const int gHeight = 20;
 
 // Tests that SkNewImageFromBitmap obeys pixelref origin.
 DEF_TEST(SkImageFromBitmap_extractSubset, reporter) {
     SkAutoTUnref<SkImage> image;
     {
         SkBitmap srcBitmap;
         srcBitmap.allocN32Pixels(gWidth, gHeight);
         srcBitmap.eraseColor(SK_ColorRED);
         SkCanvas canvas(srcBitmap);
         SkIRect r = SkIRect::MakeXYWH(5, 5, gWidth - 5, gWidth - 5);
         SkPaint p;
         p.setColor(SK_ColorGREEN);
         canvas.drawIRect(r, p);
         SkBitmap dstBitmap;
         srcBitmap.extractSubset(&dstBitmap, r);
-        image.reset(SkNewImageFromRasterBitmap(dstBitmap, true, NULL,
-                                               kUnlocked_SharedPixelRefMode));
+        image.reset(SkNewImageFromRasterBitmap(dstBitmap, NULL, kUnlocked_SharedPixelRefMode));
     }
 
     SkBitmap tgt;
     tgt.allocN32Pixels(gWidth, gHeight);
     SkCanvas canvas(tgt);
     canvas.clear(SK_ColorTRANSPARENT);
     canvas.drawImage(image, 0, 0, NULL);
 
     uint32_t pixel = 0;
     SkImageInfo info = SkImageInfo::Make(1, 1, kBGRA_8888_SkColorType, kUnpremul_SkAlphaType);
     canvas.readPixels(info, &pixel, 4, 0, 0);
     REPORTER_ASSERT(reporter, pixel == SK_ColorGREEN);
     canvas.readPixels(info, &pixel, 4, gWidth - 6, gWidth - 6);
     REPORTER_ASSERT(reporter, pixel == SK_ColorGREEN);
 
     canvas.readPixels(info, &pixel, 4, gWidth - 5, gWidth - 5);
     REPORTER_ASSERT(reporter, pixel == SK_ColorTRANSPARENT);
 }