harden requirements on SkBitmapCache

src/core/SkBitmapProcState.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmapCache.h"
 #include "SkBitmapProcState.h"
 #include "SkColorPriv.h"
@@ skipping 171 matching lines @@
                                         roundedDestWidth,
                                         roundedDestHeight,
                                         SkResourceCache::GetAllocator())) {
                 // we failed to create fScaledBitmap, so just return and let
                 // the scanline proc handle it.
                 return false;
 
             }
 
             SkASSERT(NULL != fScaledBitmap.getPixels());
+            fScaledBitmap.setImmutable();
             SkBitmapCache::Add(fOrigBitmap, roundedDestWidth, roundedDestHeight, fScaledBitmap);
         }
 
         SkASSERT(NULL != fScaledBitmap.getPixels());
         fBitmap = &fScaledBitmap;
 
         // set the inv matrix type to translate-only;
         fInvMatrix.setTranslate(fInvMatrix.getTranslateX() / fInvMatrix.getScaleX(),
                                 fInvMatrix.getTranslateY() / fInvMatrix.getScaleY());
 
@@ skipping 805 matching lines @@
     } else {
         size >>= 2;
     }
 
     if (fFilterLevel != SkPaint::kNone_FilterLevel) {
         size >>= 1;
     }
 
     return size;
 }