Build WebRTC with data channel only.

webrtc/pc/peerconnectionfactory_media_nullimpl.cc

Index: webrtc/pc/peerconnectionfactory_media_nullimpl.cc
diff --git a/webrtc/pc/peerconnectionfactory_media_nullimpl.cc b/webrtc/pc/peerconnectionfactory_media_nullimpl.cc
new file mode 100644
index 0000000000000000000000000000000000000000..d4f3daad821c07a93735f414d0197172f0d7150f
--- /dev/null
+++ b/webrtc/pc/peerconnectionfactory_media_nullimpl.cc
@@ -0,0 +1,37 @@
+/*
+ *  Copyright (c) 2017 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.
+ */
+
+#include "webrtc/media/engine/webrtcmediaengine.h"
+
+namespace webrtc {
+class AudioDecoderFactory;
+class AudioDeviceModule;
+class AudioMixer;
+}
+namespace cricket {
+class WebRtcVideoDecoderFactory;
+class WebRtcVideoEncoderFactory;
+}
+
+namespace webrtc {
+

[pthatcher, 2017/05/18 17:50:27]

I think a good name for this file may be null_media_factory.cc

[Zhi Huang, 2017/05/23 03:40:35]

Done.

+std::unique_ptr<cricket::MediaEngineInterface> CreateMediaEngineImpl(
+    webrtc::AudioDeviceModule* adm,
+    const rtc::scoped_refptr<webrtc::AudioEncoderFactory>&
+        audio_encoder_factory,
+    const rtc::scoped_refptr<webrtc::AudioDecoderFactory>&
+        audio_decoder_factory,
+    cricket::WebRtcVideoEncoderFactory* video_encoder_factory,
+    cricket::WebRtcVideoDecoderFactory* video_decoder_factory,
+    rtc::scoped_refptr<webrtc::AudioMixer> audio_mixer) {
+  return std::unique_ptr<cricket::MediaEngineInterface>();
+}
+
+}  // namespace webrtc