For unique_ptrs assigned at construction time, declare them const, and use RTC_PT_GUARDED_BY rather than RTC_GUARDED_BY. Bug: None Change-Id: I8aa83e062a1550780ee07792c1fbb195267d5524 Reviewed-on: https://webrtc-review.googlesource.com/12923 Reviewed-by: Karl Wiberg <kwiberg@webrtc.org> Reviewed-by: Philip Eliasson <philipel@webrtc.org> Commit-Queue: Niels Moller <nisse@webrtc.org> Cr-Commit-Position: refs/heads/master@{#20348}