Build WebRTC with data channel only.

webrtc/pc/peerconnection.cc

 /*
  *  Copyright 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 2317 matching lines @@
 }
 
 void PeerConnection::CreateCall_w() {
   RTC_DCHECK(!call_);
 
   const int kMinBandwidthBps = 30000;
   const int kStartBandwidthBps = 300000;
   const int kMaxBandwidthBps = 2000000;
 
   webrtc::Call::Config call_config(event_log_.get());
+  if (!factory_->channel_manager()->media_engine()) {
+    return;
+  }
   call_config.audio_state =
-      factory_->channel_manager() ->media_engine()->GetAudioState();
+      factory_->channel_manager()->media_engine()->GetAudioState();
   call_config.bitrate_config.min_bitrate_bps = kMinBandwidthBps;
   call_config.bitrate_config.start_bitrate_bps = kStartBandwidthBps;
   call_config.bitrate_config.max_bitrate_bps = kMaxBandwidthBps;
 
   call_.reset(webrtc::Call::Create(call_config));
 }
 
 }  // namespace webrtc