mojo: Make EqualsTraits<> part of public C++ API

mojo/public/cpp/bindings/lib/equals_traits.h

-// Copyright 2016 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 MOJO_PUBLIC_CPP_BINDINGS_LIB_EQUALS_TRAITS_H_
-#define MOJO_PUBLIC_CPP_BINDINGS_LIB_EQUALS_TRAITS_H_
-
-#include <type_traits>
-#include <unordered_map>
-#include <vector>
-
-#include "base/optional.h"
-#include "mojo/public/cpp/bindings/lib/template_util.h"
-
-namespace mojo {
-namespace internal {
-
-template <typename T>
-struct HasEqualsMethod {
-  template <typename U>
-  static char Test(decltype(&U::Equals));
-  template <typename U>
-  static int Test(...);
-  static const bool value = sizeof(Test<T>(0)) == sizeof(char);
-
- private:
-  EnsureTypeIsComplete<T> check_t_;
-};
-
-template <typename T, bool has_equals_method = HasEqualsMethod<T>::value>
-struct EqualsTraits;
-
-template <typename T>
-bool Equals(const T& a, const T& b);
-
-template <typename T>
-struct EqualsTraits<T, true> {
-  static bool Equals(const T& a, const T& b) { return a.Equals(b); }
-};
-
-template <typename T>
-struct EqualsTraits<T, false> {
-  static bool Equals(const T& a, const T& b) { return a == b; }
-};
-
-template <typename T>
-struct EqualsTraits<base::Optional<T>, false> {
-  static bool Equals(const base::Optional<T>& a, const base::Optional<T>& b) {
-    if (!a && !b)
-      return true;
-    if (!a || !b)
-      return false;
-
-    return internal::Equals(*a, *b);
-  }
-};
-
-template <typename T>
-struct EqualsTraits<std::vector<T>, false> {
-  static bool Equals(const std::vector<T>& a, const std::vector<T>& b) {
-    if (a.size() != b.size())
-      return false;
-    for (size_t i = 0; i < a.size(); ++i) {
-      if (!internal::Equals(a[i], b[i]))
-        return false;
-    }
-    return true;
-  }
-};
-
-template <typename K, typename V>
-struct EqualsTraits<std::unordered_map<K, V>, false> {
-  static bool Equals(const std::unordered_map<K, V>& a,
-                     const std::unordered_map<K, V>& b) {
-    if (a.size() != b.size())
-      return false;
-    for (const auto& element : a) {
-      auto iter = b.find(element.first);
-      if (iter == b.end() || !internal::Equals(element.second, iter->second))
-        return false;
-    }
-    return true;
-  }
-};
-
-template <typename T>
-bool Equals(const T& a, const T& b) {
-  return EqualsTraits<T>::Equals(a, b);
-}
-
-}  // namespace internal
-}  // namespace mojo
-
-#endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_EQUALS_TRAITS_H_