Stop cast streaming API without start

chrome/renderer/media/cast_rtp_stream.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/renderer/media/cast_rtp_stream.h"
 
 #include "base/bind.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
 #include "base/memory/weak_ptr.h"
@@ skipping 492 matching lines @@
         base::Bind(&CastRtpStream::DidEncounterError,
                    weak_factory_.GetWeakPtr()));
     start_callback.Run();
   }
 }
 
 void CastRtpStream::Stop() {
   VLOG(1) << "CastRtpStream::Stop =  " << (IsAudio() ? "audio" : "video");
   audio_sink_.reset();
   video_sink_.reset();
-  stop_callback_.Run();
+  if (!stop_callback_.is_null())
+    stop_callback_.Run();
 }
 
 void CastRtpStream::ToggleLogging(bool enable) {
   cast_session_->ToggleLogging(IsAudio(), enable);
 }
 
 void CastRtpStream::GetRawEvents(
     const base::Callback<void(scoped_ptr<base::BinaryValue>)>& callback,
     const std::string& extra_data) {
   cast_session_->GetEventLogsAndReset(IsAudio(), extra_data, callback);
 }
 
 void CastRtpStream::GetStats(
     const base::Callback<void(scoped_ptr<base::DictionaryValue>)>& callback) {
   cast_session_->GetStatsAndReset(IsAudio(), callback);
 }
 
 bool CastRtpStream::IsAudio() const {
   return track_.source().type() == blink::WebMediaStreamSource::TypeAudio;
 }
 
 void CastRtpStream::DidEncounterError(const std::string& message) {
   // Save the WeakPtr first because the error callback might delete this object.
   base::WeakPtr<CastRtpStream> ptr = weak_factory_.GetWeakPtr();
   error_callback_.Run(message);
   content::RenderThread::Get()->GetMessageLoop()->PostTask(
       FROM_HERE,
       base::Bind(&CastRtpStream::Stop, ptr));
 }