SkImage_Raster's pixels are always immutable.

src/image/SkImage.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 "SkBitmap.h"
 #include "SkCanvas.h"
 #include "SkData.h"
@@ skipping 236 matching lines @@
             }
             unrefCopy.reset(tex);
         }
         const SkImageInfo info = bm.info();
         return SkNEW_ARGS(SkImage_Gpu, (info.width(), info.height(), info.alphaType(),
                                         tex, 0, SkSurface::kNo_Budgeted));
     }
 #endif
 
     // This will check for immutable (share or copy)
-    return SkNewImageFromRasterBitmap(bm, false, nullptr, kUnlocked_SharedPixelRefMode);
+    return SkNewImageFromRasterBitmap(bm, nullptr, kUnlocked_SharedPixelRefMode);
 }
 
 bool SkImage::asLegacyBitmap(SkBitmap* bitmap, LegacyBitmapMode mode) const {
     return as_IB(this)->onAsLegacyBitmap(bitmap, mode);
 }
 
 bool SkImage_Base::onAsLegacyBitmap(SkBitmap* bitmap, LegacyBitmapMode mode) const {
     // As the base-class, all we can do is make a copy (regardless of mode).
     // Subclasses that want to be more optimal should override.
     SkImageInfo info = SkImageInfo::MakeN32(this->width(), this->height(),
@@ skipping 23 matching lines @@
 
 SkImage* SkImage::NewFromAdoptedTexture(GrContext*, const GrBackendTextureDesc&, SkAlphaType) {
     return NULL;
 }
 
 SkImage* SkImage::NewFromTextureCopy(GrContext*, const GrBackendTextureDesc&, SkAlphaType) {
     return NULL;
 }
 
 #endif