Chromium	61.0.3133.0 (Developer Build) (64-bit)
Revision	a1b0694ea3efca7ad5ffd529f5261df80ab49c07-refs/heads/master@{#480203}
OS	Linux

Chromium debug build build run with --load-media-router-component-extension=1 and "Media Remoting during Cast Tab Mirroring" flag enabled. Cast device is a ChromeCast.

What steps will reproduce the problem?
(1) Open a .webm file with ctrl-o
(2) Start casting with tab mirror
(3) full size the tab
(4) Media remoting kicks in
(5) browser goes kaput. 

[1:12:0616/160620.034692:FATAL:ffmpeg_demuxer.cc(690)] Check failed: false. Proprietary codecs not enabled.
#0 0x7f3cc76babeb base::debug::StackTrace::StackTrace()
#1 0x7f3cc76b98ec base::debug::StackTrace::StackTrace()
#2 0x7f3cc772d463 logging::LogMessage::~LogMessage()
#3 0x7f3cbd160e6d media::FFmpegDemuxerStream::EnableBitstreamConverter()
#4 0x7f3cc1fe3086 media::remoting::DemuxerStreamAdapter::EnableBitstreamConverter()
#5 0x7f3cc1fe1108 media::remoting::DemuxerStreamAdapter::OnReceivedRpc()
...
#16 0x7f3cc76c083e base::debug::TaskAnnotator::RunTask()
#17 0x7f3cc775753d base::MessageLoop::RunTask()
#18 0x7f3cc77577c7 base::MessageLoop::DeferOrRunPendingTask()
#19 0x7f3cc7757adf base::MessageLoop::DoWork()
#20 0x7f3cc776a128 base::MessagePumpDefault::Run()
#21 0x7f3cc7756f08 base::MessageLoop::Run()
#22 0x7f3cc78012cd base::RunLoop::Run()
#23 0x7f3cc78b8c94 base::Thread::Run()
#24 0x7f3cc78b94fa base::Thread::ThreadMain()
#25 0x7f3cc789a89a base::(anonymous namespace)::ThreadFunc()
#26 0x7f3cc7b51184 start_thread
#27 0x7f3cad945bed clone