gbm: make NativePixmap RefCountedThreadSafe

ui/ozone/public/native_pixmap.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_OZONE_PUBLIC_NATIVE_PIXMAP_H_
 #define UI_OZONE_PUBLIC_NATIVE_PIXMAP_H_
 
 #include "base/memory/ref_counted.h"
 
 namespace ui {
 
 // This represents a buffer that can be directly imported via GL for
 // rendering, or exported via dma-buf fds.
-class NativePixmap : public base::RefCounted<NativePixmap> {
+class NativePixmap : public base::RefCountedThreadSafe<NativePixmap> {
  public:
   NativePixmap() {}
 
   virtual void* /* EGLClientBuffer */ GetEGLClientBuffer() = 0;
   virtual int GetDmaBufFd() = 0;
   virtual int GetDmaBufPitch() = 0;
 
  protected:
   virtual ~NativePixmap() {}
 
-  friend class base::RefCounted<NativePixmap>;
+ private:
+  friend class base::RefCountedThreadSafe<NativePixmap>;
 
   DISALLOW_COPY_AND_ASSIGN(NativePixmap);
 };
 
 }  // namespace ui
 
 #endif  // UI_OZONE_PUBLIC_NATIVE_PIXMAP_H_