Pass u2f message callback vector as a const reference

device/u2f/u2f_request_unittest.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 <list>
 
 #include "base/memory/ptr_util.h"
 #include "base/run_loop.h"
 #include "base/test/test_io_thread.h"
 #include "device/base/mock_device_client.h"
@@ skipping 27 matching lines @@
 };
 }  // namespace
 
 class TestResponseCallback {
  public:
   TestResponseCallback()
       : callback_(base::Bind(&TestResponseCallback::ReceivedCallback,
                              base::Unretained(this))) {}
   ~TestResponseCallback() {}
 
-  void ReceivedCallback(U2fReturnCode status, std::vector<uint8_t> data) {
+  void ReceivedCallback(U2fReturnCode status,
+                        const std::vector<uint8_t>& data) {
     closure_.Run();
   }
 
   void WaitForCallback() {
     closure_ = run_loop_.QuitClosure();
     run_loop_.Run();
   }
 
   U2fRequest::ResponseCallback& callback() { return callback_; }
 
@@ skipping 91 matching lines @@
   c_info.usage = HidUsageAndPage(1, static_cast<HidUsageAndPage::Page>(0xf1d0));
   scoped_refptr<HidDeviceInfo> u2f_device = make_scoped_refptr(
       new HidDeviceInfo(kTestDeviceId0, 0, 0, "Test Fido Device", "123FIDO",
                         kHIDBusTypeUSB, c_info, 64, 64, 0));
   hid_service->AddDevice(u2f_device);
   cb.WaitForCallback();
   EXPECT_EQ(U2fRequest::State::BUSY, request.state_);
 }
 
 }  // namespace device