Pass u2f message callback vector as a const reference

device/u2f/u2f_sign.cc

 // Copyright 2017 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 "u2f_sign.h"
 
 #include "base/memory/ptr_util.h"
 
 namespace device {
 
@@ skipping 34 matching lines @@
   }
   // Try signing current device with the first registered key
   auto it = registered_keys_.cbegin();
   current_device_->Sign(
       app_param_, challenge_hash_, *it,
       base::Bind(&U2fSign::OnTryDevice, weak_factory_.GetWeakPtr(), it));
 }
 
 void U2fSign::OnTryDevice(std::vector<std::vector<uint8_t>>::const_iterator it,
                           U2fReturnCode return_code,
-                          std::vector<uint8_t> response_data) {
+                          const std::vector<uint8_t>& response_data) {
   switch (return_code) {
     case U2fReturnCode::SUCCESS:
       state_ = State::COMPLETE;
       cb_.Run(return_code, response_data);
       break;
     case U2fReturnCode::CONDITIONS_NOT_SATISFIED: {
       // Key handle is accepted by this device, but waiting on user touch. Move
       // on and try this device again later.
       state_ = State::IDLE;
       Transition();
@@ skipping 17 matching lines @@
     default:
       // Some sort of failure occured. Abandon this device and move on.
       state_ = State::IDLE;
       current_device_ = nullptr;
       Transition();
       break;
   }
 }
 
 }  // namespace device