Tame the proliferation of UserContext constructors

chrome/browser/chromeos/login/managed/supervised_user_authentication.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/chromeos/login/managed/supervised_user_authentication.h"
 
 #include "base/base64.h"
 #include "base/json/json_file_value_serializer.h"
 #include "base/macros.h"
 #include "base/metrics/histogram.h"
@@ skipping 107 matching lines @@
     holder.GetStringWithoutPathExpansion(kSalt, &salt);
     DCHECK(!salt.empty());
     return BuildPasswordForHashWithSaltSchema(salt, password);
   }
   NOTREACHED();
   return password;
 }
 
 UserContext SupervisedUserAuthentication::TransformPasswordInContext(
     const UserContext& context) {
-  UserContext result;
-  result.CopyFrom(context);
+  UserContext result = context;
   int user_schema = GetPasswordSchema(context.GetUserID());
   if (user_schema == SCHEMA_PLAIN)
     return result;
 
   if (user_schema == SCHEMA_SALT_HASHED) {
     base::DictionaryValue holder;
     std::string salt;
     owner_->GetPasswordInformation(context.GetUserID(), &holder);
     holder.GetStringWithoutPathExpansion(kSalt, &salt);
     DCHECK(!salt.empty());
@@ skipping 211 matching lines @@
     LOG(FATAL) << "HMAC::Sign failed";
 
   std::string raw_result(out_bytes, out_bytes + sizeof(out_bytes));
 
   std::string result;
   base::Base64Encode(raw_result, &result);
   return result;
 }
 
 }  // namespace chromeos