Unified callback system.

base/template_util.h

Index: base/template_util.h
diff --git a/base/template_util.h b/base/template_util.h
index 27bdb7348890571b1e7628ba1c908dfab330afa9..765358d58459297006b669da126c59e6728bac14 100644
--- a/base/template_util.h
+++ b/base/template_util.h
@@ -27,6 +27,14 @@ typedef integral_constant<bool, false> false_type;
 template <class T> struct is_pointer : false_type {};
 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 {};
+
 namespace internal {
 
 // Types small_ and big_ are guaranteed such that sizeof(small_) <