Add base::UnguessableToken << operator

base/unguessable_token.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_UNGUESSABLE_TOKEN_H_
 #define BASE_UNGUESSABLE_TOKEN_H_
 
 #include <stdint.h>
 #include <string.h>
+#include <iosfwd>
 #include <tuple>
 
 #include "base/base_export.h"
 #include "base/hash.h"
 #include "base/logging.h"
 
 namespace base {
 
 struct UnguessableTokenHash;
 
@@ skipping 59 matching lines @@
  private:
   friend struct UnguessableTokenHash;
   UnguessableToken(uint64_t high, uint64_t low);
 
   // Note: Two uint64_t are used instead of uint8_t[16], in order to have a
   // simpler ToString() and is_empty().
   uint64_t high_ = 0;
   uint64_t low_ = 0;
 };
 
+BASE_EXPORT std::ostream& operator<<(std::ostream& out,
+                                     const UnguessableToken& token);
+
 // For use in std::unordered_map.
 struct UnguessableTokenHash {
   size_t operator()(const base::UnguessableToken& token) const {
     DCHECK(token);
     return base::HashInts64(token.high_, token.low_);
   }
 };
 
 }  // namespace base
 
 #endif  // BASE_UNGUESSABLE_TOKEN_H_