XFA: merge patch from CL 729293003, use FX_ArraySize for safety

core/include/fxcrt/fx_basic.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 _FX_BASIC_H_
 #define _FX_BASIC_H_
 #ifndef _FX_SYSTEM_H_
 #include "fx_system.h"
 #endif
 #ifndef _FX_MEMORY_H_
 #include "fx_memory.h"
 #endif
 #ifndef _FX_STRING_H_
 #include "fx_string.h"
 #endif
 #ifndef _FX_STREAM_H_
 #include "fx_stream.h"
 #endif
+
+// 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];
+
 class CFX_BinaryBuf : public CFX_Object
 {
 public:
     CFX_BinaryBuf();
     CFX_BinaryBuf(FX_STRSIZE size);
 
     ~CFX_BinaryBuf();
 
     void                                        Clear();
 
@@ skipping 1594 matching lines @@
     FX_FLOAT c;
     FX_FLOAT d;
     FX_FLOAT e;
     FX_FLOAT f;
     FX_FLOAT g;
     FX_FLOAT h;
     FX_FLOAT i;
 };
 
 #endif