Add a Retained Pointer smart class.

core/fxcrt/include/cfx_retain_ptr.h

+// Copyright 2016 PDFium 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 CORE_FXCRT_INCLUDE_CFX_RETAIN_PTR_H_
+#define CORE_FXCRT_INCLUDE_CFX_RETAIN_PTR_H_
+
+#include <memory>
+
+#include "core/include/fxcrt/fx_memory.h"
+
+template <class T>
+class CFX_RetainPtr {
+ public:
+  explicit CFX_RetainPtr(T* pObj) : m_pObj(pObj) {
+    if (m_pObj)
+      m_pObj->Retain();
+  }
+
+  CFX_RetainPtr() : CFX_RetainPtr(nullptr) {}
+  CFX_RetainPtr(const CFX_RetainPtr& that) : CFX_RetainPtr(that.Get()) {}
+  CFX_RetainPtr(CFX_RetainPtr&& that) { Swap(that); }
+
+  template <class U>
+  CFX_RetainPtr(const CFX_RetainPtr<U>& that)
+      : CFX_RetainPtr(that.Get()) {}
+
+  void Reset(T* obj = nullptr) {

[Lei Zhang, 2016/03/29 18:36:36]

Would it be slightly cheaper to do this instead to avoid creating |tmp| ?

if (obj)
  obj->Retain();
m_pObj.reset(obj)

[Tom Sepez, 2016/03/29 21:37:22]

Done.

+    CFX_RetainPtr<T> tmp(obj);
+    Swap(tmp);
+  }
+
+  T* Get() const { return m_pObj.get(); }
+  void Swap(CFX_RetainPtr& that) { m_pObj.swap(that.m_pObj); }
+
+  CFX_RetainPtr& operator=(const CFX_RetainPtr& that) {
+    if (*this != that)
+      Reset(that.Get());
+    return *this;
+  }
+
+  bool operator==(const CFX_RetainPtr& that) const {
+    return Get() == that.Get();
+  }
+
+  bool operator!=(const CFX_RetainPtr& that) const { return !(*this == that); }
+
+  operator bool() const { return !!m_pObj; }
+  T& operator*() const { return *m_pObj.get(); }
+  T* operator->() const { return m_pObj.get(); }
+
+ private:
+  std::unique_ptr<T, ReleaseDeleter<T>> m_pObj;
+};
+
+#endif  // CORE_FXCRT_INCLUDE_CFX_RETAIN_PTR_H_