cache private readback for gpu-images

include/core/SkPixelRef.h

 /*
  * Copyright 2008 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.
  */
 
 #ifndef SkPixelRef_DEFINED
 #define SkPixelRef_DEFINED
 
@@ skipping 361 matching lines @@
     friend class SkSurface_Raster;   // For the two methods above.
 
     bool isPreLocked() const { return fPreLocked; }
     friend class SkImage_Raster;
 
     // When copying a bitmap to another with the same shape and config, we can safely
     // clone the pixelref generation ID too, which makes them equivalent under caching.
     friend class SkBitmap;  // only for cloneGenID
     void cloneGenID(const SkPixelRef&);
 
+    void setImmutableWithID(uint32_t genID);
+    friend class SkImage_Gpu;
+
     typedef SkRefCnt INHERITED;
 };
 
 class SkPixelRefFactory : public SkRefCnt {
 public:
     /**
      *  Allocate a new pixelref matching the specified ImageInfo, allocating
      *  the memory for the pixels. If the ImageInfo requires a ColorTable,
      *  the pixelref will ref() the colortable.
      *  On failure return NULL.
      */
     virtual SkPixelRef* create(const SkImageInfo&, size_t rowBytes, SkColorTable*) = 0;
 };
 
 #endif