Add skeleton circular queue file.

base/template_util.h

Index: base/template_util.h
diff --git a/base/template_util.h b/base/template_util.h
index 0cf1477cf9a57b2e7326f5de40dae60f73bb4aa8..fb48b5a95459eee4f865dcd65d5c19ef53541eac 100644
--- a/base/template_util.h
+++ b/base/template_util.h
@@ -7,6 +7,7 @@
 
 #include <stddef.h>
 #include <iosfwd>
+#include <iterator>
 #include <type_traits>
 #include <utility>
 
@@ -40,6 +41,19 @@ template <class T> struct is_non_const_reference : std::false_type {};
 template <class T> struct is_non_const_reference<T&> : std::true_type {};
 template <class T> struct is_non_const_reference<const T&> : std::false_type {};
 
+template <typename...>
+struct make_void {
+  using type = void;
+};
+
+// A clone of C++17 std::void_t.
+// Unlike the original version, we need |make_void| as a helper struct to avoid
+// a C++14 defect.
+// ref: http://en.cppreference.com/w/cpp/types/void_t
+// ref: http://open-std.org/JTC1/SC22/WG21/docs/cwg_defects.html#1558
+template <typename... Ts>
+using void_t = typename make_void<Ts...>::type;
+
 namespace internal {
 
 template <typename...>
@@ -64,6 +78,17 @@ struct SupportsOstreamOperator<T,
                                              << std::declval<T>()))>
     : std::true_type {};
 
+// Used to detech whether the given type is an iterator.  This is normally used
+// with std::enable_if to provide disambiguation for functions that take
+// templatzed iterators as input.
+template <typename T, typename = void>
+struct is_iterator : std::false_type {};
+
+template <typename T>
+struct is_iterator<T,
+                   void_t<typename std::iterator_traits<T>::iterator_category>>
+    : std::true_type {};
+
 }  // namespace internal
 
 // is_trivially_copyable is especially hard to get right.