chrome: Add out-of-line copy ctors for complex classes.

chrome/browser/extensions/api/identity/extension_token_key.cc

 // Copyright 2013 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.
 
 #include "chrome/browser/extensions/api/identity/extension_token_key.h"
 
 #include <tuple>
 
 namespace extensions {
 
 ExtensionTokenKey::ExtensionTokenKey(const std::string& extension_id,
                                      const std::string& account_id,
                                      const std::set<std::string>& scopes)
     : extension_id(extension_id), account_id(account_id), scopes(scopes) {}
 
+ExtensionTokenKey::ExtensionTokenKey(const ExtensionTokenKey& other) = default;
+
 ExtensionTokenKey::~ExtensionTokenKey() {}
 
 bool ExtensionTokenKey::operator<(const ExtensionTokenKey& rhs) const {
   return std::tie(extension_id, account_id, scopes) <
     std::tie(rhs.extension_id, rhs.account_id, rhs.scopes);
 }
 
 }  // namespace extensions