Use SkNVRefCnt for a couple common types.

include/core/SkData.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkData_DEFINED
 #define SkData_DEFINED
 
 #include <stdio.h>
 
 #include "SkRefCnt.h"
 
 class SkStream;
 
 /**
  *  SkData holds an immutable data buffer. Not only is the data immutable,
  *  but the actual ptr that is returned (by data() or bytes()) is guaranteed
  *  to always be the same for the life of this instance.
  */
-class SK_API SkData : public SkRefCnt {
+class SK_API SkData : public SkNVRefCnt<SkData> {

[reed1, 2016/08/09 18:36:59]

can we mark SkData as final?

 public:
     /**
      *  Returns the number of bytes stored.
      */
     size_t size() const { return fSize; }
 
     bool isEmpty() const { return 0 == fSize; }
 
     /**
      *  Returns the ptr to the data.
@@ skipping 39 matching lines @@
      *  Function that, if provided, will be called when the SkData goes out
      *  of scope, allowing for custom allocation/freeing of the data's contents.
      */
     typedef void (*ReleaseProc)(const void* ptr, void* context);
 
     /**
      *  Create a new dataref by copying the specified data
      */
     static sk_sp<SkData> MakeWithCopy(const void* data, size_t length);
 
-    
+
     /**
      *  Create a new data with uninitialized contents. The caller should call writable_data()
      *  to write into the buffer, but this must be done before another ref() is made.
      */
     static sk_sp<SkData> MakeUninitialized(size_t length);
 
     /**
      *  Create a new dataref by copying the specified c-string
      *  (a null-terminated array of bytes). The returned SkData will have size()
      *  equal to strlen(cstr) + 1. If cstr is NULL, it will be treated the same
@@ skipping 58 matching lines @@
      */
     static sk_sp<SkData> MakeSubset(const SkData* src, size_t offset, size_t length);
 
     /**
      *  Returns a new empty dataref (or a reference to a shared empty dataref).
      *  New or shared, the caller must see that unref() is eventually called.
      */
     static sk_sp<SkData> MakeEmpty();
 
 private:
+    friend class SkNVRefCnt<SkData>;
     ReleaseProc fReleaseProc;
     void*       fReleaseProcContext;
     void*       fPtr;
     size_t      fSize;
 
     SkData(const void* ptr, size_t size, ReleaseProc, void* context);
     explicit SkData(size_t size);   // inplace new/delete
-    virtual ~SkData();
+    ~SkData();
 
 
     // Objects of this type are sometimes created in a custom fashion using sk_malloc_throw and
     // therefore must be sk_freed. We overload new to also call sk_malloc_throw so that memory
     // can be unconditionally released using sk_free in an overloaded delete. Overloading regular
     // new means we must also overload placement new.
     void* operator new(size_t size) { return sk_malloc_throw(size); }
     void* operator new(size_t, void* p) { return p; }
     void operator delete(void* p) { sk_free(p); }
 
     // Called the first time someone calls NewEmpty to initialize the singleton.
     friend SkData* sk_new_empty_data();
 
     // shared internal factory
     static sk_sp<SkData> PrivateNewWithCopy(const void* srcOrNull, size_t length);
 
     static void DummyReleaseProc(const void*, void*); // {}
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif