Pass u2f message callback vector as a const reference

device/u2f/u2f_device.h

 // 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.
 
 #ifndef DEVICE_U2F_U2F_DEVICE_H_
 #define DEVICE_U2F_U2F_DEVICE_H_
 
 #include <vector>
 
 #include "base/callback.h"
 #include "base/memory/weak_ptr.h"
 #include "u2f_apdu_response.h"
 #include "u2f_return_code.h"
 
 namespace device {
 
 class U2fApduCommand;
 
 // Device abstraction for an individual U2F device. A U2F device defines the
 // standardized Register, Sign, and GetVersion methods.
 class U2fDevice {
  public:
   enum class ProtocolVersion {
     U2F_V2,
     UNKNOWN,
   };
 
   using MessageCallback =
-      base::Callback<void(U2fReturnCode, std::vector<uint8_t>)>;
+      base::Callback<void(U2fReturnCode, const std::vector<uint8_t>&)>;
   using VersionCallback =
       base::Callback<void(bool success, ProtocolVersion version)>;
   using DeviceCallback =
       base::Callback<void(bool success,
                           std::unique_ptr<U2fApduResponse> response)>;
   using WinkCallback = base::Callback<void()>;
 
   virtual ~U2fDevice();
 
   // Raw messages parameters are defined by the specification at
@@ skipping 42 matching lines @@
   void OnWink(const WinkCallback& callback,
               bool success,
               std::unique_ptr<U2fApduResponse> response);
 
   DISALLOW_COPY_AND_ASSIGN(U2fDevice);
 };
 
 }  // namespace device
 
 #endif  // DEVICE_U2F_U2F_DEVICE_H_