Add a web reference to arraysize() macro docs.

base/macros.h

 // Copyright 2014 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.
 
 // This file contains macros and macro-like constructs (e.g., templates) that
 // are commonly used throughout Chromium source. (It may also contain things
 // that are closely related to things that are commonly used that belong in this
 // file.)
 
 #ifndef BASE_MACROS_H_
@@ skipping 19 matching lines @@
 // A macro to disallow all the implicit constructors, namely the
 // default constructor, copy constructor and operator= functions.
 //
 // This should be used in the private: declarations for a class
 // that wants to prevent anyone from instantiating it. This is
 // especially useful for classes containing only static methods.
 #define DISALLOW_IMPLICIT_CONSTRUCTORS(TypeName) \
   TypeName() = delete;                           \
   DISALLOW_COPY_AND_ASSIGN(TypeName)
 
-// The 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 arraysize on
-// a pointer by mistake, you will get a compile-time error.
+// The 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 arraysize on a pointer by mistake, you
+// will get a compile-time error.  For the technical details, refer to
+// http://blogs.msdn.com/b/the1/archive/2004/05/07/128242.aspx.
 
 // This template function declaration is used in defining 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];
 #define arraysize(array) (sizeof(ArraySizeHelper(array)))
 
 // bit_cast<Dest,Source> is a template function that implements the
 // equivalent of "*reinterpret_cast<Dest*>(&source)".  We need this in
 // very low-level functions like the protobuf library and fast math
@@ skipping 88 matching lines @@
 
 // Use these to declare and define a static local variable (static T;) so that
 // it is leaked so that its destructors are not called at exit. If you need
 // thread-safe initialization, use base/lazy_instance.h instead.
 #define CR_DEFINE_STATIC_LOCAL(type, name, arguments) \
   static type& name = *new type arguments
 
 }  // base
 
 #endif  // BASE_MACROS_H_