Revert "Move webrtc/{base => rtc_base}" (https://codereview.webrtc.org/2877023002)

Will reland in two different commits to preserve git blame history.

BUG=webrtc:7634
NOTRY=True
TBR=kwiberg@webrtc.org

Change-Id: I550da8525aeb9c5b8f96338fcf1c9714f3dcdab1
Reviewed-on: https://chromium-review.googlesource.com/554610
Reviewed-by: Henrik Kjellander <kjellander@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#18820}

webrtc/base/template_util.h

@@ -13,9 +13,115 @@
 #ifndef WEBRTC_BASE_TEMPLATE_UTIL_H_
 #define WEBRTC_BASE_TEMPLATE_UTIL_H_
 
+#include <stddef.h>  // For size_t.
 
-// This header is deprecated and is just left here temporarily during
-// refactoring. See https://bugs.webrtc.org/7634 for more details.
-#include "webrtc/rtc_base/template_util.h"
+namespace rtc {
+
+// Template definitions from tr1.
+
+template<class T, T v>
+struct integral_constant {
+  static const T value = v;
+  typedef T value_type;
+  typedef integral_constant<T, v> type;
+};
+
+template <class T, T v> const T integral_constant<T, v>::value;
+
+typedef integral_constant<bool, true> true_type;
+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 T, class U> struct is_same : public false_type {};
+template <class T> struct is_same<T, 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 {};
+
+// Helper useful for converting a tuple to variadic template function
+// arguments.
+//
+// sequence_generator<3>::type will be sequence<0, 1, 2>.
+template <int...>
+struct sequence {};
+template <int N, int... S>
+struct sequence_generator : sequence_generator<N - 1, N - 1, S...> {};
+template <int... S>
+struct sequence_generator<0, S...> {
+  typedef sequence<S...> type;
+};
+
+namespace internal {
+
+// Types YesType and NoType are guaranteed such that sizeof(YesType) <
+// sizeof(NoType).
+typedef char YesType;
+
+struct NoType {
+  YesType dummy[2];
+};
+
+// This class is an implementation detail for is_convertible, and you
+// don't need to know how it works to use is_convertible. For those
+// who care: we declare two different functions, one whose argument is
+// of type To and one with a variadic argument list. We give them
+// return types of different size, so we can use sizeof to trick the
+// compiler into telling us which function it would have chosen if we
+// had called it with an argument of type From.  See Alexandrescu's
+// _Modern C++ Design_ for more details on this sort of trick.
+
+struct ConvertHelper {
+  template <typename To>
+  static YesType Test(To);
+
+  template <typename To>
+  static NoType Test(...);
+
+  template <typename From>
+  static From& Create();
+};
+
+// Used to determine if a type is a struct/union/class. Inspired by Boost's
+// is_class type_trait implementation.
+struct IsClassHelper {
+  template <typename C>
+  static YesType Test(void(C::*)(void));
+
+  template <typename C>
+  static NoType Test(...);
+};
+
+}  // namespace internal
+
+// Inherits from true_type if From is convertible to To, false_type otherwise.
+//
+// Note that if the type is convertible, this will be a true_type REGARDLESS
+// of whether or not the conversion would emit a warning.
+template <typename From, typename To>
+struct is_convertible
+    : integral_constant<bool,
+                        sizeof(internal::ConvertHelper::Test<To>(
+                                   internal::ConvertHelper::Create<From>())) ==
+                        sizeof(internal::YesType)> {
+};
+
+template <typename T>
+struct is_class
+    : integral_constant<bool,
+                        sizeof(internal::IsClassHelper::Test<T>(0)) ==
+                            sizeof(internal::YesType)> {
+};
+
+}  // namespace rtc
 
 #endif  // WEBRTC_BASE_TEMPLATE_UTIL_H_