Limit target encoder bitrate change frequency in the frame scheduler.

remoting/protocol/webrtc_connection_to_host.cc

Index: remoting/protocol/webrtc_connection_to_host.cc
diff --git a/remoting/protocol/webrtc_connection_to_host.cc b/remoting/protocol/webrtc_connection_to_host.cc
index 1e0c78878df2742c8b2c8b9469ae6faf8db45f79..27b662b2767c93ba678fed2aa0afdcb96c5e84c4 100644
--- a/remoting/protocol/webrtc_connection_to_host.cc
+++ b/remoting/protocol/webrtc_connection_to_host.cc
@@ -37,7 +37,8 @@ void WebrtcConnectionToHost::Connect(
   transport_.reset(new WebrtcTransport(
       jingle_glue::JingleThreadWrapper::current(), transport_context, this));
 
-  transport_->audio_module()->SetAudioTaskRunner(audio_decode_task_runner_);
+  if (audio_decode_task_runner_)
+    transport_->audio_module()->SetAudioTaskRunner(audio_decode_task_runner_);
 
   session_ = std::move(session);
   session_->SetEventHandler(this);