Reuse WeakFactory from U2fDevice derived classes

device/u2f/mock_u2f_device.h

Index: device/u2f/mock_u2f_device.h
diff --git a/device/u2f/mock_u2f_device.h b/device/u2f/mock_u2f_device.h
index f4e65da0524418633169f24d71ed0e8c4e996eca..fcd7b27af9d9eb6c7a9e4d3e717fe5274d5a2603 100644
--- a/device/u2f/mock_u2f_device.h
+++ b/device/u2f/mock_u2f_device.h
@@ -29,6 +29,7 @@ class MockU2fDevice : public U2fDevice {
                void(U2fApduCommand* command, const DeviceCallback& cb));
   void DeviceTransact(std::unique_ptr<U2fApduCommand> command,
                       const DeviceCallback& cb) override;
+  base::WeakPtr<U2fDevice> GetWeakPtr() override;
   static void TransactNoError(std::unique_ptr<U2fApduCommand> command,
                               const DeviceCallback& cb);
   static void NotSatisfied(U2fApduCommand* cmd, const DeviceCallback& cb);
@@ -36,6 +37,9 @@ class MockU2fDevice : public U2fDevice {
   static void NoErrorSign(U2fApduCommand* cmd, const DeviceCallback& cb);
   static void NoErrorRegister(U2fApduCommand* cmd, const DeviceCallback& cb);
   static void WinkDoNothing(const WinkCallback& cb);
+
+ private:
+  base::WeakPtrFactory<U2fDevice> weak_factory_;
 };
 
 }  // namespace device