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

core/include/fxcrt/fx_basic.h

Index: core/include/fxcrt/fx_basic.h
diff --git a/core/include/fxcrt/fx_basic.h b/core/include/fxcrt/fx_basic.h
index 0c84f540e9d17985b8da126b569171322fa83f9d..2a77e6e9473ca7b2d0ec40ee6222881c938698da 100644
--- a/core/include/fxcrt/fx_basic.h
+++ b/core/include/fxcrt/fx_basic.h
@@ -18,6 +18,22 @@
 #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: