Build WebRTC with data channel only.

webrtc/pc/channelmanager.cc

Index: webrtc/pc/channelmanager.cc
diff --git a/webrtc/pc/channelmanager.cc b/webrtc/pc/channelmanager.cc
index 995a07bf0562c6de6e43f000104be5934b4a5f60..5f377f274b313a9b995d1c44db7cd93ee50ff00f 100644
--- a/webrtc/pc/channelmanager.cc
+++ b/webrtc/pc/channelmanager.cc
@@ -141,14 +141,19 @@ bool ChannelManager::Init() {
         rtc::Bind(&rtc::Thread::SetAllowBlockingCalls, network_thread_, false));
   }
 
+#ifdef HAVE_MEDIA
   initialized_ = worker_thread_->Invoke<bool>(
       RTC_FROM_HERE, Bind(&ChannelManager::InitMediaEngine_w, this));
+#else
+  initialized_ = true;
+#endif
   RTC_DCHECK(initialized_);
   return initialized_;
 }
 
 bool ChannelManager::InitMediaEngine_w() {
   RTC_DCHECK(worker_thread_ == rtc::Thread::Current());
+  RTC_DCHECK(media_engine_);
   return media_engine_->Init();
 }
 
@@ -222,6 +227,9 @@ VoiceChannel* ChannelManager::CreateVoiceChannel_w(
   RTC_DCHECK(worker_thread_ == rtc::Thread::Current());
   RTC_DCHECK(nullptr != media_controller);
 
+#ifndef HAVE_MEDIA
+  return nullptr;
+#endif
   VoiceMediaChannel* media_channel = media_engine_->CreateChannel(
       media_controller->call_w(), media_controller->config(), options);
   if (!media_channel)