Pass u2f message callback vector as a const reference

device/u2f/u2f_register.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_register.h"
 
 #include "base/memory/ptr_util.h"
 
 namespace device {
 
@@ skipping 20 matching lines @@
 
 void U2fRegister::TryDevice() {
   DCHECK(current_device_);
 
   current_device_->Register(
       app_param_, challenge_hash_,
       base::Bind(&U2fRegister::OnTryDevice, weak_factory_.GetWeakPtr()));
 }
 
 void U2fRegister::OnTryDevice(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);

[Reilly Grant (use Gerrit), 2017/04/26 00:11:02]

U2fRequest::ResponseCallback should also be updated to prevent a copy here.

[piperc, 2017/04/26 00:19:55]

Will the caller need to do a move of the data before the U2fRequest goes out of
scope? 

[Reilly Grant (use Gerrit), 2017/04/26 00:28:00]

The function bound to |cb_| is called from inside this stack frame so
|response_data| will still be valid.

[Casey Piper, 2017/04/26 00:39:05]

Right. Makes sense.
Done.

       break;
     case U2fReturnCode::CONDITIONS_NOT_SATISFIED:
       // Waiting for user touch, move on and try this device later
       state_ = State::IDLE;
       Transition();
       break;
     default:
       state_ = State::IDLE;
       // An error has occured, quit trying this device
       current_device_ = nullptr;
       Transition();
       break;
   }
 }
 
 }  // namespace device