Reuse WeakFactory from U2fDevice derived classes

device/u2f/mock_u2f_device.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 "mock_u2f_device.h"
 
 namespace device {
 
-MockU2fDevice::MockU2fDevice() {}
+MockU2fDevice::MockU2fDevice() : weak_factory_(this) {}
 
 MockU2fDevice::~MockU2fDevice() {}
 
 void MockU2fDevice::DeviceTransact(std::unique_ptr<U2fApduCommand> command,
                                    const DeviceCallback& cb) {
   DeviceTransactPtr(command.get(), cb);
 }
 
 // static
 void MockU2fDevice::NotSatisfied(U2fApduCommand* cmd,
@@ skipping 23 matching lines @@
   cb.Run(true, base::MakeUnique<U2fApduResponse>(
                    std::vector<uint8_t>({kRegister}),
                    U2fApduResponse::Status::SW_NO_ERROR));
 }
 
 // static
 void MockU2fDevice::WinkDoNothing(const WinkCallback& cb) {
   cb.Run();
 }
 
+base::WeakPtr<U2fDevice> MockU2fDevice::GetWeakPtr() {
+  return weak_factory_.GetWeakPtr();
+}
+
 }  // namespace device