The return type of PacketSource::NextPacket() is changed from a naked pointer to an std::uniqe_ptr. The interface contract was and still is that the ownership is passed from the callee to the caller, but a unique_ptr makes this explicit. BUG=webrtc:2692 Review-Url: https://codereview.webrtc.org/2005873002 Cr-Commit-Position: refs/heads/master@{#12884}