[CrOS PhoneHub] Copy by value in ConnectToDeviceOperationBase

This code previously had erroneously stored  a DeviceIdPair by
reference, meaning that the field could potentially be referring to
deleted memory. This is a potential culprit for an issue which causes
authentication to fail in the SecureChannel protocol.

Bug: 1157278
Change-Id: I97589e7e94865fb0f841a8adbe19dffb9d2e0a06
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2585589
Commit-Queue: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: Josh Nohle <nohle@chromium.org>
Auto-Submit: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: Josh Nohle <nohle@chromium.org>
Cr-Commit-Position: refs/heads/master@{#835881}

chromeos/services/secure_channel/connect_to_device_operation_base.h

@@ -104,7 +104,7 @@ class ConnectToDeviceOperationBase
   const DeviceIdPair& device_id_pair() const { return device_id_pair_; }
 
  private:
-  const DeviceIdPair& device_id_pair_;
+  DeviceIdPair device_id_pair_;
   scoped_refptr<base::TaskRunner> task_runner_;
   base::Optional<ConnectionPriority> pending_connection_attempt_priority_;
   base::WeakPtrFactory<ConnectToDeviceOperationBase> weak_ptr_factory_{this};