Build WebRTC with data channel only.

webrtc/pc/nullmediafactory.cc

Index: webrtc/pc/nullmediafactory.cc
diff --git a/webrtc/pc/nullmediafactory.cc b/webrtc/pc/nullmediafactory.cc
new file mode 100644
index 0000000000000000000000000000000000000000..48cf1600843e5eab4b88763215bcca9e4a1fc458
--- /dev/null
+++ b/webrtc/pc/nullmediafactory.cc
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+/*
+ *  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/logging/rtc_event_log/rtc_event_log.h"
+#include "webrtc/media/engine/webrtcmediaengine.h"
+
+namespace webrtc {
+class AudioDecoderFactory;
+class AudioDeviceModule;
+class AudioMixer;
+}  // namespace webrtc
+
+namespace cricket {
+
+MediaEngineInterface* WebRtcMediaEngineFactory::Create(
+    webrtc::AudioDeviceModule* adm,
+    const rtc::scoped_refptr<webrtc::AudioEncoderFactory>&
+        audio_encoder_factory,
+    const rtc::scoped_refptr<webrtc::AudioDecoderFactory>&
+        audio_decoder_factory,
+    WebRtcVideoEncoderFactory* video_encoder_factory,
+    WebRtcVideoDecoderFactory* video_decoder_factory,
+    rtc::scoped_refptr<webrtc::AudioMixer> audio_mixer) {
+  return nullptr;
+}
+
+}  // namespace cricket
+
+namespace webrtc {
+
+std::unique_ptr<RtcEventLog> RtcEventLog::Create() {
+  return std::unique_ptr<RtcEventLog>(new RtcEventLogNullImpl());
+}
+
+Call* Call::Create(const Call::Config& config) {
+  return nullptr;
+}
+
+}  // namespace webrtc