Support binding WeakPtr<> to methods with void return types.

base/template_util.h

-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 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.
 
 #ifndef BASE_TEMPLATE_UTIL_H_
 #define BASE_TEMPLATE_UTIL_H_
 #pragma once
 
 #include <cstddef>  // For size_t.
 
 #include "build/build_config.h"
@@ skipping 18 matching lines @@
 template <class T> struct is_pointer<T*> : true_type {};
 
 template<class> struct is_array : public false_type {};
 template<class T, size_t n> struct is_array<T[n]> : public true_type {};
 template<class T> struct is_array<T[]> : public true_type {};
 
 template <class T> struct is_non_const_reference : false_type {};
 template <class T> struct is_non_const_reference<T&> : true_type {};
 template <class T> struct is_non_const_reference<const T&> : false_type {};
 
+template <class T> struct is_void : false_type {};
+template <> struct is_void<void> : true_type {};
+
 namespace internal {
 
 // Types YesType and NoType are guaranteed such that sizeof(YesType) <
 // sizeof(NoType).
 typedef char YesType;
 
 struct NoType {
   YesType dummy[2];
 };
 
@@ skipping 44 matching lines @@
 template <typename T>
 struct is_class
     : integral_constant<bool,
                         sizeof(internal::IsClassHelper::Test<T>(0)) ==
                             sizeof(internal::YesType)> {
 };
 
 }  // namespace base
 
 #endif  // BASE_TEMPLATE_UTIL_H_