Cleanup return values in http_auth

net/http/http_auth_handler.h

 // Copyright (c) 2011 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 NET_HTTP_HTTP_AUTH_HANDLER_H_
 #define NET_HTTP_HTTP_AUTH_HANDLER_H_
 
 #include <string>
 
 #include "net/base/completion_callback.h"
@@ skipping 69 matching lines @@
   HttpAuth::Scheme auth_scheme() const {
     return auth_scheme_;
   }
 
   // The realm, encoded as UTF-8. This may be empty.
   const std::string& realm() const {
     return realm_;
   }
 
   // The challenge which was issued when creating the handler.
-  const std::string challenge() const {
-    return auth_challenge_;
-  }
+  const std::string& challenge() const { return auth_challenge_; }
 
   // Numeric rank based on the challenge's security level. Higher
   // numbers are better. Used by HttpAuth::ChooseBestChallenge().
   int score() const {
     return score_;
   }
 
   HttpAuth::Target target() const {
     return target_;
   }
@@ skipping 87 matching lines @@
  private:
   void OnGenerateAuthTokenComplete(int rv);
   void FinishGenerateAuthToken();
 
   CompletionCallback callback_;
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_HTTP_AUTH_HANDLER_H_