Repro steps:
1. Start meeting at meet.google.com (using google.com account if necessary). I used 68.0.3418.2 (Official Build) dev for this, shouldn't matter.
2. Navigate to meeting from a dcheck-enabled ToT build (I used refs/heads/master@{#556719}).
3. Allow access to microphone.

I don't have a microphone or camera connected (don't think it matters).
I may be in some Meet dogfoods, LMK if you can't repro.

+Helen since you wrote the code.

Crash repros every time.
[176113:176150:0508/153513.184069:FATAL:proxy_resolving_client_socket.cc(278)] Check failed: !socket_handle_->socket(). 
#0 0x7fdf128e721d base::debug::StackTrace::StackTrace()
#1 0x7fdf126114bc base::debug::StackTrace::StackTrace()
#2 0x7fdf12682fba logging::LogMessage::~LogMessage()
#3 0x7fdf06d2a299 network::ProxyResolvingClientSocket::DoInitConnection()
#4 0x7fdf06d28eed network::ProxyResolvingClientSocket::DoLoop()
#5 0x7fdf06d29f31 network::ProxyResolvingClientSocket::OnIOComplete()
#6 0x7fdf06c828cf _ZN4base8internal13FunctorTraitsIMN7network31ChunkedDataPipeUploadDataStreamEFvjEvE6InvokeIS5_PS3_JjEEEvT_OT0_DpOT1_
#7 0x7fdf06c8282f _ZN4base8internal12InvokeHelperILb0EvE8MakeItSoIRKMN7network31ChunkedDataPipeUploadDataStreamEFvjEJPS5_jEEEvOT_DpOT0_
#8 0x7fdf06c827c5 _ZN4base8internal7InvokerINS0_9BindStateIMN7network31ChunkedDataPipeUploadDataStreamEFvjEJNS0_17UnretainedWrapperIS4_EEEEEFvjEE7RunImplIRKS6_RKNSt3__15tupleIJS8_EEEJLm0EEEEvOT_OT0_NSF_16integer_sequenceImJXspT1_EEEEOj
#9 0x7fdf06c8274b _ZN4base8internal7InvokerINS0_9BindStateIMN7network31ChunkedDataPipeUploadDataStreamEFvjEJNS0_17UnretainedWrapperIS4_EEEEEFvjEE3RunEPNS0_13BindStateBaseEj
#10 0x7fdf0fc5c72e _ZNKR4base17RepeatingCallbackIFviEE3RunEi
#11 0x7fdf100d7587 net::ProxyResolutionService::Request::QueryComplete()
#12 0x7fdf0fb933df _ZN4base8internal13FunctorTraitsIMN3net18ClientSocketHandleEFviEvE6InvokeIS5_PS3_JiEEEvT_OT0_DpOT1_
#13 0x7fdf0fb9333f _ZN4base8internal12InvokeHelperILb0EvE8MakeItSoIRKMN3net18ClientSocketHandleEFviEJPS5_iEEEvOT_DpOT0_
#14 0x7fdf0fb932d5 _ZN4base8internal7InvokerINS0_9BindStateIMN3net18ClientSocketHandleEFviEJNS0_17UnretainedWrapperIS4_EEEEEFviEE7RunImplIRKS6_RKNSt3__15tupleIJS8_EEEJLm0EEEEvOT_OT0_NSF_16integer_sequenceImJXspT1_EEEEOi
#15 0x7fdf0fb9320b _ZN4base8internal7InvokerINS0_9BindStateIMN3net18ClientSocketHandleEFviEJNS0_17UnretainedWrapperIS4_EEEEEFviEE3RunEPNS0_13BindStateBaseEi
#16 0x7fdf06c7fdce _ZNKR4base17RepeatingCallbackIFvjEE3RunEj
#17 0x7fdf06d91544 network::(anonymous namespace)::ProxyResolverMojo::Job::CompleteRequest()
#18 0x7fdf06d90988 network::(anonymous namespace)::ProxyResolverMojo::Job::ReportResult()
#19 0x7fdf06effff2 proxy_resolver::mojom::ProxyResolverRequestClientStubDispatch::Accept()
#20 0x7fdf06d94933 proxy_resolver::mojom::ProxyResolverRequestClientStub<>::Accept()
#21 0x7fdf10a2ec45 mojo::InterfaceEndpointClient::HandleValidatedMessage()
#22 0x7fdf10a2d691 mojo::InterfaceEndpointClient::HandleIncomingMessageThunk::Accept()
#23 0x7fdf10a2bb22 mojo::FilterChain::Accept()
#24 0x7fdf10a31875 mojo::InterfaceEndpointClient::HandleIncomingMessage()
#25 0x7fdf10a3ddab mojo::internal::MultiplexRouter::ProcessIncomingMessage()
#26 0x7fdf10a3d2f5 mojo::internal::MultiplexRouter::Accept()
#27 0x7fdf10a2bb22 mojo::FilterChain::Accept()
#28 0x7fdf10a1d9df mojo::Connector::ReadSingleMessage()
#29 0x7fdf10a1ea2a mojo::Connector::ReadAllAvailableMessages()
#30 0x7fdf10a1e7f5 mojo::Connector::OnHandleReadyInternal()
#31 0x7fdf10a1e6db mojo::Connector::OnWatcherHandleReady()
#32 0x7fdf10a222bf _ZN4base8internal13FunctorTraitsIMN4mojo9ConnectorEFvjEvE6InvokeIS5_PS3_JjEEEvT_OT0_DpOT1_
#33 0x7fdf10a2221f _ZN4base8internal12InvokeHelperILb0EvE8MakeItSoIRKMN4mojo9ConnectorEFvjEJPS5_jEEEvOT_DpOT0_
#34 0x7fdf10a221b5 _ZN4base8internal7InvokerINS0_9BindStateIMN4mojo9ConnectorEFvjEJNS0_17UnretainedWrapperIS4_EEEEEFvjEE7RunImplIRKS6_RKNSt3__15tupleIJS8_EEEJLm0EEEEvOT_OT0_NSF_16integer_sequenceImJXspT1_EEEEOj
#35 0x7fdf10a220eb _ZN4base8internal7InvokerINS0_9BindStateIMN4mojo9ConnectorEFvjEJNS0_17UnretainedWrapperIS4_EEEEEFvjEE3RunEPNS0_13BindStateBaseEj
#36 0x7fdf10a1909e _ZNKR4base17RepeatingCallbackIFvjEE3RunEj
#37 0x7fdf10a2132f mojo::SimpleWatcher::DiscardReadyState()
#38 0x7fdf10a215af _ZN4base8internal13FunctorTraitsIPFvRKNS_17RepeatingCallbackIFvjEEEjRKN4mojo18HandleSignalsStateEEvE6InvokeIRKSC_JS6_jSA_EEEvOT_DpOT0_
#39 0x7fdf10a2154d _ZN4base8internal12InvokeHelperILb0EvE8MakeItSoIRKPFvRKNS_17RepeatingCallbackIFvjEEEjRKN4mojo18HandleSignalsStateEEJS8_jSC_EEEvOT_DpOT0_
#40 0x7fdf10a214f0 _ZN4base8internal7InvokerINS0_9BindStateIPFvRKNS_17RepeatingCallbackIFvjEEEjRKN4mojo18HandleSignalsStateEEJS5_EEEFvjSB_EE7RunImplIRKSD_RKNSt3__15tupleIJS5_EEEJLm0EEEEvOT_OT0_NSK_16integer_sequenceImJXspT1_EEEEOjSB_
#41 0x7fdf10a21426 _ZN4base8internal7InvokerINS0_9BindStateIPFvRKNS_17RepeatingCallbackIFvjEEEjRKN4mojo18HandleSignalsStateEEJS5_EEEFvjSB_EE3RunEPNS0_13BindStateBaseEjSB_
#42 0x7fdf109b070e _ZNKR4base17RepeatingCallbackIFvjRKN4mojo18HandleSignalsStateEEE3RunEjS4_
#43 0x7fdf109b0059 mojo::SimpleWatcher::OnHandleReady()
#44 0x7fdf109b08a6 mojo::SimpleWatcher::Context::Notify()
#45 0x7fdf109b021f mojo::SimpleWatcher::Context::CallNotify()
#46 0x7fdf06b5d167 mojo::edk::WatcherDispatcher::InvokeWatchCallback()
#47 0x7fdf06b5c8e0 mojo::edk::Watch::InvokeCallback()
#48 0x7fdf06b4d3f9 mojo::edk::RequestContext::~RequestContext()
#49 0x7fdf06b1cecd mojo::edk::NodeChannel::OnChannelMessage()
#50 0x7fdf06aee48e mojo::edk::Channel::OnReadComplete()
#51 0x7fdf06b712c9 mojo::edk::(anonymous namespace)::ChannelPosix::OnFileCanReadWithoutBlocking()
#52 0x7fdf1292051e base::MessagePumpLibevent::FdWatchController::OnFileCanReadWithoutBlocking()
#53 0x7fdf12921df0 base::MessagePumpLibevent::OnLibeventNotification()
#54 0x7fdf129761fe event_process_active
#55 0x7fdf12975847 event_base_loop
#56 0x7fdf12921f71 base::MessagePumpLibevent::Run()
#57 0x7fdf126aae8b base::MessageLoop::Run()
#58 0x7fdf12753ead base::RunLoop::Run()
#59 0x7fdf12805d78 base::Thread::Run()
#60 0x7fdf0c120c6f content::BrowserProcessSubThread::IOThreadRun()
#61 0x7fdf0c120b6a content::BrowserProcessSubThread::Run()