Implement Optional::has_value() and Optional::reset().

base/optional.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 BASE_OPTIONAL_H_
 #define BASE_OPTIONAL_H_
 
 #include <type_traits>
 
 #include "base/logging.h"
@@ skipping 145 matching lines @@
   T& operator*() & { return value(); }
 
   constexpr const T&& operator*() const&& { return std::move(value()); }
 
   // TODO(mlamouri): using 'constexpr' here breaks compiler that assume it was
   // meant to be 'constexpr const'.
   T&& operator*() && { return std::move(value()); }
 
   constexpr explicit operator bool() const { return !storage_.is_null_; }
 
+  constexpr bool has_value() const { return !storage_.is_null_; }
+
   // TODO(mlamouri): using 'constexpr' here breaks compiler that assume it was
   // meant to be 'constexpr const'.
   T& value() & {
     DCHECK(!storage_.is_null_);
     return *storage_.buffer_.template data_as<T>();
   }
 
   // TODO(mlamouri): can't use 'constexpr' with DCHECK.
   const T& value() const& {
     DCHECK(!storage_.is_null_);
@@ skipping 48 matching lines @@
         FreeIfNeeded();
       }
       return;
     }
 
     DCHECK(!storage_.is_null_ && !other.storage_.is_null_);
     using std::swap;
     swap(**this, *other);
   }
 
+  void reset() {
+    FreeIfNeeded();
+  }
+
   template <class... Args>
   void emplace(Args&&... args) {
     FreeIfNeeded();
     Init(std::forward<Args>(args)...);
   }
 
  private:
   void Init(const T& value) {
     DCHECK(storage_.is_null_);
     new (storage_.buffer_.void_data()) T(value);
@@ skipping 204 matching lines @@
 template <class T>
 struct hash<base::Optional<T>> {
   size_t operator()(const base::Optional<T>& opt) const {
     return opt == base::nullopt ? 0 : std::hash<T>()(*opt);
   }
 };
 
 }  // namespace std
 
 #endif  // BASE_OPTIONAL_H_