ui: Add ref-counting to GLFence class.

ui/gl/gl_fence_libsync.h

 // Copyright 2016 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_GL_GL_FENCE_LIBSYNC_H_
 #define UI_GL_GL_FENCE_LIBSYNC_H_
 
 #include "base/file_descriptor_posix.h"
 #include "base/files/scoped_file.h"
 #include "base/macros.h"
 #include "ui/gl/gl_export.h"
 #include "ui/gl/gl_fence.h"
 
 namespace gl {
 
 class GL_EXPORT GLFenceLibsync : public GLFence {
  public:
   explicit GLFenceLibsync(base::ScopedFD fd);
-  ~GLFenceLibsync() override;
 
   // Overridden from GLFence:
   bool HasCompleted() override;
   void ClientWait() override;
   void ServerWait() override;
 
  private:
+  ~GLFenceLibsync() override;
+
   base::ScopedFD fd_;
 
   DISALLOW_COPY_AND_ASSIGN(GLFenceLibsync);
 };
 
 }  // namespace gl
 
 #endif  // UI_GL_GL_FENCE_LIBSYNC_H_