Detailed description will be added.

webrtc/pc/channelmanager.cc

Index: webrtc/pc/channelmanager.cc
diff --git a/webrtc/pc/channelmanager.cc b/webrtc/pc/channelmanager.cc
index af6e3c7e99e16f9780c4872ee8384a2d006e71df..1817f6923334a896649dd5848ee628a05b3e9c3f 100644
--- a/webrtc/pc/channelmanager.cc
+++ b/webrtc/pc/channelmanager.cc
@@ -89,21 +89,33 @@ bool ChannelManager::SetVideoRtxEnabled(bool enable) {
 
 void ChannelManager::GetSupportedAudioSendCodecs(
     std::vector<AudioCodec>* codecs) const {
+  if (!media_engine_) {
+    return;
+  }
   *codecs = media_engine_->audio_send_codecs();
 }
 
 void ChannelManager::GetSupportedAudioReceiveCodecs(
     std::vector<AudioCodec>* codecs) const {
+  if (!media_engine_) {
+    return;
+  }
   *codecs = media_engine_->audio_recv_codecs();
 }
 
 void ChannelManager::GetSupportedAudioRtpHeaderExtensions(
     RtpHeaderExtensions* ext) const {
+  if (!media_engine_) {
+    return;
+  }
   *ext = media_engine_->GetAudioCapabilities().header_extensions;
 }
 
 void ChannelManager::GetSupportedVideoCodecs(
     std::vector<VideoCodec>* codecs) const {
+  if (!media_engine_) {
+    return;
+  }
   codecs->clear();
 
   std::vector<VideoCodec> video_codecs = media_engine_->video_codecs();
@@ -118,11 +130,17 @@ void ChannelManager::GetSupportedVideoCodecs(
 
 void ChannelManager::GetSupportedVideoRtpHeaderExtensions(
     RtpHeaderExtensions* ext) const {
+  if (!media_engine_) {
+    return;
+  }
   *ext = media_engine_->GetVideoCapabilities().header_extensions;
 }
 
 void ChannelManager::GetSupportedDataCodecs(
     std::vector<DataCodec>* codecs) const {
+  if (!data_media_engine_) {
+    return;
+  }
   *codecs = data_media_engine_->data_codecs();
 }
 
@@ -148,7 +166,10 @@ bool ChannelManager::Init() {
 
 bool ChannelManager::InitMediaEngine_w() {
   RTC_DCHECK(worker_thread_ == rtc::Thread::Current());
-  return media_engine_->Init();
+  if (media_engine_) {
+    return media_engine_->Init();
+  }
+  return true;
 }
 
 void ChannelManager::Terminate() {
@@ -223,6 +244,9 @@ VoiceChannel* ChannelManager::CreateVoiceChannel_w(
   RTC_DCHECK(initialized_);
   RTC_DCHECK(worker_thread_ == rtc::Thread::Current());
   RTC_DCHECK(nullptr != call);
+  if (!media_engine_) {
+    return nullptr;
+  }
 
   VoiceMediaChannel* media_channel = media_engine_->CreateChannel(
       call, media_config, options);