Add an Android-framework-only stable ID to SkPixelRef.

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 109 matching lines @@
      *  modifications will be lost when unlockPixels() is called.)
      */
     bool lockPixelsAreWritable() const;
 
     /** Returns a non-zero, unique value corresponding to the pixels in this
         pixelref. Each time the pixels are changed (and notifyPixelsChanged is
         called), a different generation ID will be returned.
     */
     uint32_t getGenerationID() const;
 
+#ifdef SK_BUILD_FOR_ANDROID_FRAMEWORK
+    /** Returns a non-zero, unique value corresponding to this SkPixelRef.
+        Unlike the generation ID, this ID remains the same even when the pixels
+        are changed. IDs are not reused (until uint32_t wraps), so it is safe
+        to consider this ID unique even after this SkPixelRef is deleted.
+
+        Can be used as a key which uniquely identifies this SkPixelRef
+        regardless of changes to its pixels or deletion of this object.
+     */
+    uint32_t getStableID() const { return fStableID; }
+#endif
+
     /**
      *  Call this if you have changed the contents of the pixels. This will in-
      *  turn cause a different generation ID value to be returned from
      *  getGenerationID().
      */
     void notifyPixelsChanged();
 
     /**
      *  Change the info's AlphaType. Note that this does not automatically
      *  invalidate the generation ID. If the pixel values themselves have
@@ skipping 211 matching lines @@
 
     // mostly const. fInfo.fAlpahType can be changed at runtime.
     const SkImageInfo fInfo;
 
     // LockRec is only valid if we're in a locked state (isLocked())
     LockRec         fRec;
     int             fLockCount;
 
     mutable SkTRacy<uint32_t> fGenerationID;
     mutable SkTRacy<bool>     fUniqueGenerationID;
+#ifdef SK_BUILD_FOR_ANDROID_FRAMEWORK
+    const uint32_t fStableID;
+#endif
 
     SkTDArray<GenIDChangeListener*> fGenIDChangeListeners;  // pointers are owned
 
     SkString    fURI;
 
     // can go from false to true, but never from true to false
     bool    fIsImmutable;
     // only ever set in constructor, const after that
     bool    fPreLocked;
 
@@ skipping 15 matching lines @@
     /**
      *  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