Add element_type, swap, operators, fix reset on sk_sp.

include/private/SkTLogic.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  *
  *
  * This header provides some of the helpers (like std::enable_if_t) which will
  * become available with C++14 in the type_traits header (in the skstd
  * namespace). This header also provides several Skia specific additions such
@@ skipping 44 matching lines @@
 #endif
 #endif
 template <typename R, typename... Args> struct is_function<R(Args..., ...)> : std::true_type {};
 
 template <typename T> using add_const_t = typename std::add_const<T>::type;
 template <typename T> using add_volatile_t = typename std::add_volatile<T>::type;
 template <typename T> using add_cv_t = typename std::add_cv<T>::type;
 template <typename T> using add_pointer_t = typename std::add_pointer<T>::type;
 template <typename T> using add_lvalue_reference_t = typename std::add_lvalue_reference<T>::type;
 
+template <typename... T> using common_type_t = typename std::common_type<T...>::type;
+
 template <typename S, typename D,
           bool=std::is_void<S>::value || is_function<D>::value || std::is_array<D>::value>
 struct is_convertible_detector {
     static const/*expr*/ bool value = std::is_void<D>::value;
 };
 template <typename S, typename D> struct is_convertible_detector<S, D, false> {
     using yes_type = uint8_t;
     using no_type = uint16_t;
 
     template <typename To> static void param_convertable_to(To);
@@ skipping 43 matching lines @@
 template <typename D, typename S> using same_volatile_t = typename same_volatile<D, S>::type;
 template <typename D, typename S> using same_cv = copy_cv<skstd::remove_cv_t<D>, S>;
 template <typename D, typename S> using same_cv_t = typename same_cv<D, S>::type;
 
 }  // namespace sknonstd
 
 // Just a pithier wrapper for enable_if_t.
 #define SK_WHEN(condition, T) skstd::enable_if_t<!!(condition), T>
 
 #endif