message: Fix destruction order of PortAllocator and PacketSocketFactory.
  PortAllocator depends on PacketSocketFactory, so it should be deleted
  afterwords in case its created sockets depend on the resources owned
  by the factory.
  Cr-Commit-Position: refs/heads/master@{#32020}
diff: @@ -1184,10 +1184,10 @@ class PeerConnection : public PeerConnectionInternal,
  // is not injected. It should be required once chromium supplies it.
  std::unique_ptr<AsyncResolverFactory> async_resolver_factory_
  RTC_GUARDED_BY(signaling_thread());
  + std::unique_ptr<rtc::PacketSocketFactory> packet_socket_factory_;
  std::unique_ptr<cricket::PortAllocator>
  port_allocator_; // TODO(bugs.webrtc.org/9987): Accessed on both
  // signaling and network thread.
  - std::unique_ptr<rtc::PacketSocketFactory> packet_socket_factory_;
  std::unique_ptr<webrtc::IceTransportFactory>
  ice_transport_factory_; // TODO(bugs.webrtc.org/9987): Accessed on the
  // signaling thread but the underlying raw
  