Add a Retained Pointer smart class.

core/fxcrt/include/fx_memory.h

 // Copyright 2014 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.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #ifndef CORE_FXCRT_INCLUDE_FX_MEMORY_H_
 #define CORE_FXCRT_INCLUDE_FX_MEMORY_H_
 
 #include "core/fxcrt/include/fx_system.h"
@@ skipping 56 matching lines @@
 #define FX_Realloc(type, ptr, size) \
   (type*) FX_ReallocOrDie(ptr, size, sizeof(type))
 
 // May return NULL.
 #define FX_TryAlloc(type, size) (type*) calloc(size, sizeof(type))
 #define FX_TryRealloc(type, ptr, size) \
   (type*) FX_SafeRealloc(ptr, size, sizeof(type))
 
 #define FX_Free(ptr) free(ptr)
 
+// The FX_ArraySize(arr) macro returns the # of elements in an array arr.
+// The expression is a compile-time constant, and therefore can be
+// used in defining new arrays, for example.  If you use FX_ArraySize on
+// a pointer by mistake, you will get a compile-time error.
+//
+// One caveat is that FX_ArraySize() doesn't accept any array of an
+// anonymous type or a type defined inside a function.
+#define FX_ArraySize(array) (sizeof(ArraySizeHelper(array)))
+
+// This template function declaration is used in defining FX_ArraySize.
+// Note that the function doesn't need an implementation, as we only
+// use its type.
+template <typename T, size_t N>
+char(&ArraySizeHelper(T(&array)[N]))[N];
+
+// Used with std::unique_ptr to FX_Free raw memory.
+struct FxFreeDeleter {
+  inline void operator()(void* ptr) const { FX_Free(ptr); }
+};
+
+// Used with std::unique_ptr to Release() objects that can't be deleted.
+template <class T>
+struct ReleaseDeleter {
+  inline void operator()(T* ptr) const { ptr->Release(); }
+};
+
 class CFX_DestructObject {
  public:
   virtual ~CFX_DestructObject() {}
 };
 
 #endif  // __cplusplus
 
 #endif  // CORE_FXCRT_INCLUDE_FX_MEMORY_H_