Please help triage the flake. Here's a typical failure:

[ RUN      ] WebRtcGetUserMediaBrowserTest.VideoInIFrameAndCloseInSuccessCb
Xlib:  extension "RANDR" missing on display ":99".
DevTools listening on ws://127.0.0.1:42895/devtools/browser/182681c0-04d3-4cc4-9e86-ca7721dc813d
Fontconfig warning: "/etc/fonts/fonts.conf", line 146: blank doesn't take any effect anymore. please remove it from your fonts.conf
[27141:27163:0131/063108.344875:FATAL:media_stream_manager.cc(638)] Check failed: false.
#0 0x000003bc1a6c base::debug::StackTrace::StackTrace()
#1 0x000003be057c logging::LogMessage::~LogMessage()
#2 0x00000340a41c content::MediaStreamManager::CancelRequest()
#3 0x000003404d33 content::MediaStreamDispatcherHost::CancelRequest()
#4 0x000001d76a93 content::mojom::MediaStreamDispatcherHostStubDispatch::Accept()
#5 0x00000390de87 mojo::InterfaceEndpointClient::HandleValidatedMessage()
#6 0x00000390da26 mojo::FilterChain::Accept()
#7 0x00000390f352 mojo::InterfaceEndpointClient::HandleIncomingMessage()
#8 0x00000391c36a mojo::internal::MultiplexRouter::ProcessIncomingMessage()
#9 0x00000391b843 mojo::internal::MultiplexRouter::Accept()
#10 0x00000390da26 mojo::FilterChain::Accept()
#11 0x00000390cacd mojo::Connector::ReadSingleMessage()
#12 0x00000390d574 mojo::Connector::ReadAllAvailableMessages()
#13 0x00000390d3d6 mojo::Connector::OnHandleReadyInternal()
#14 0x00000231c944 content::(anonymous namespace)::InitializeErrorCallback()
#15 0x000004243665 mojo::SimpleWatcher::OnHandleReady()
#16 0x000004243b07 mojo::SimpleWatcher::Context::Notify()
#17 0x000004242564 mojo::SimpleWatcher::Context::CallNotify()
#18 0x0000039018c2 mojo::edk::Watch::InvokeCallback()
#19 0x0000038fcc84 mojo::edk::RequestContext::~RequestContext()
#20 0x0000038fb5ff mojo::edk::NodeChannel::OnChannelMessage()
#21 0x0000038f9baa mojo::edk::Channel::OnReadComplete()
#22 0x0000039070f9 mojo::edk::(anonymous namespace)::ChannelPosix::OnFileCanReadWithoutBlocking()
#23 0x000003bee14f base::MessagePumpLibevent::OnLibeventNotification()
#24 0x000003c8be1d event_base_loop
#25 0x000003bee3ee base::MessagePumpLibevent::Run()
#26 0x000003be839c base::MessageLoop::Run()
#27 0x000003c12236 base::RunLoop::Run()
#28 0x000003c4693a base::Thread::Run()
#29 0x0000030d90b8 content::BrowserThreadImpl::IOThreadRun()
#30 0x0000030d92d1 content::BrowserThreadImpl::Run()
#31 0x000003c46f33 base::Thread::ThreadMain()
#32 0x000003c402ef base::(anonymous namespace)::ThreadFunc()
#33 0x7f057b262184 start_thread
#34 0x7f0576a40ffd clone

Hitting the NOTREACHED() in this function:

void MediaStreamManager::CancelRequest(int render_process_id,
                                       int render_frame_id,
                                       int page_request_id) {
  DCHECK_CURRENTLY_ON(BrowserThread::IO);
  for (const LabeledDeviceRequest& labeled_request : requests_) {
    DeviceRequest* const request = labeled_request.second;
    if (request->requesting_process_id == render_process_id &&
        request->requesting_frame_id == render_frame_id &&
        request->page_request_id == page_request_id) {
      CancelRequest(labeled_request.first);
      return;
    }
  }
  NOTREACHED();
}

Detected 5 new flakes for test/step "WebRtcGetUserMediaBrowserTest.VideoInIFrameAndCloseInSuccessCb". To see the actual flakes, please visit https://chromium-try-flakes.appspot.com/all_flake_occurrences?key=ahVzfmNocm9taXVtLXRyeS1mbGFrZXNySQsSBUZsYWtlIj5XZWJSdGNHZXRVc2VyTWVkaWFCcm93c2VyVGVzdC5WaWRlb0luSUZyYW1lQW5kQ2xvc2VJblN1Y2Nlc3NDYgw. This message was posted automatically by the chromium-try-flakes app. Since flakiness is ongoing, the issue was moved back into Sheriff Bug Queue (unless already there).

This seems really flaky. I'm going to disable the test for now.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/629745ea96114586f186a0e4147fd0814726e731

commit 629745ea96114586f186a0e4147fd0814726e731
Author: Yuta Kitamura <yutak@chromium.org>
Date: Mon Feb 05 06:07:24 2018

Disable WebRtcGetUserMediaBrowserTest.VideoInIFrameAndCloseInSuccessCb on Linux and ChromeOS.

This test is flaky.

TBR=sfiera@chromium.org

Bug: 807638
Change-Id: I1879a2864db1d3d679bf70966bc52c98ab6fb67e
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/899890
Reviewed-by: Yuta Kitamura <yutak@chromium.org>
Commit-Queue: Yuta Kitamura <yutak@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534337}
[modify] https://crrev.com/629745ea96114586f186a0e4147fd0814726e731/content/browser/webrtc/webrtc_getusermedia_browsertest.cc

OK, now we want a real owner of this issue.

CCing random folks who may know better...

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ab6ba58e04db64b9276cbc3cda578831009924f2

commit ab6ba58e04db64b9276cbc3cda578831009924f2
Author: Oleh Prypin <oprypin@chromium.org>
Date: Tue Feb 27 12:49:25 2018

Disable VideoInIFrameAndCloseInSuccessCb browser test

It's also flaky on Android, so disable on all platforms

Bug: chromium:807638
No-Try: True
Change-Id: I0b7dc9cb14198c590538f3a8125e47636fc2c1d7
Reviewed-on: https://chromium-review.googlesource.com/939162
Commit-Queue: Oleh Prypin <oprypin@chromium.org>
Reviewed-by: Patrik Höglund <phoglund@chromium.org>
Cr-Commit-Position: refs/heads/master@{#539423}
[modify] https://crrev.com/ab6ba58e04db64b9276cbc3cda578831009924f2/content/browser/webrtc/webrtc_getusermedia_browsertest.cc