Fix DCHECK in the chromoting host when disconnecting a WebRTC connection.

remoting/protocol/webrtc_transport.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "remoting/protocol/webrtc_transport.h"
 
 #include <string>
 #include <utility>
 #include <vector>
 
@@ skipping 190 matching lines @@
 
     peer_connection_ = peer_connection_factory_->CreatePeerConnection(
         rtc_config, &constraints, std::move(port_allocator), nullptr, this);
   }
   virtual ~PeerConnectionWrapper() {
     // PeerConnection creates threads internally, which are stopped when the
     // connection is closed. Thread.Stop() is a blocking operation.
     // See crbug.com/660081.
     base::ThreadRestrictions::ScopedAllowIO allow_io;
     peer_connection_->Close();
+    peer_connection_ = nullptr;
+    peer_connection_factory_ = nullptr;
+    audio_module_ = nullptr;
   }
 
   WebrtcAudioModule* audio_module() {
     return audio_module_.get();
   }
 
   webrtc::PeerConnectionInterface* peer_connection() {
     return peer_connection_.get();
   }
 
@@ skipping 497 matching lines @@
   // the stack and so it must be destroyed later.
   base::ThreadTaskRunnerHandle::Get()->DeleteSoon(
       FROM_HERE, peer_connection_wrapper_.release());
 
   if (error != OK)
     event_handler_->OnWebrtcTransportError(error);
 }
 
 }  // namespace protocol
 }  // namespace remoting