I just got this DCHECK on trunk (r507022) after signing in to a test account in a new profile.

[61233:61233:1006/165231.113526:FATAL:interface_endpoint_client.cc(32)] Check failed: !is_valid. The callback passed to EmbeddedSearch::HistorySyncCheck() was never run.
#0 0x7f39f6d44d5d base::debug::StackTrace::StackTrace()
#1 0x7f39f6d4318c base::debug::StackTrace::StackTrace()
#2 0x7f39f6dc9d5a logging::LogMessage::~LogMessage()
#3 0x7f39f51d6a24 mojo::(anonymous namespace)::DCheckIfInvalid()
#4 0x7f39f51d6871 mojo::(anonymous namespace)::ResponderThunk::DCheckInvalid()
#5 0x0014b87b7a1c chrome::mojom::EmbeddedSearch_HistorySyncCheck_ProxyToResponder::~EmbeddedSearch_HistorySyncCheck_ProxyToResponder()
#6 0x0014b87b7360 base::internal::PassedWrapper<>::~PassedWrapper()
#7 0x0014b87b78d5 std::__1::__tuple_leaf<>::~__tuple_leaf()
#8 0x0014b87b78b5 _ZNSt3__112__tuple_implINS_15__tuple_indicesIJLm0EEEEJN4base8internal13PassedWrapperINS_10unique_ptrIN6chrome5mojom48EmbeddedSearch_HistorySyncCheck_ProxyToResponderENS_14default_deleteIS9_EEEEEEEED2Ev
#9 0x0014b87b7895 _ZNSt3__15tupleIJN4base8internal13PassedWrapperINS_10unique_ptrIN6chrome5mojom48EmbeddedSearch_HistorySyncCheck_ProxyToResponderENS_14default_deleteIS7_EEEEEEEED2Ev
#10 0x0014b87b7863 _ZN4base8internal9BindStateIMN6chrome5mojom48EmbeddedSearch_HistorySyncCheck_ProxyToResponderEFvbEJNS0_13PassedWrapperINSt3__110unique_ptrIS4_NS8_14default_deleteIS4_EEEEEEEED2Ev
#11 0x0014b87b7827 _ZN4base8internal9BindStateIMN6chrome5mojom48EmbeddedSearch_HistorySyncCheck_ProxyToResponderEFvbEJNS0_13PassedWrapperINSt3__110unique_ptrIS4_NS8_14default_deleteIS4_EEEEEEEE7DestroyEPKNS0_13BindStateBaseE
#12 0x7f39f6cf65a5 base::internal::BindStateBaseRefCountTraits::Destruct()
#13 0x7f39f6cf7078 base::RefCountedThreadSafe<>::Release()
#14 0x7f39f6cf7035 scoped_refptr<>::Release()
#15 0x7f39f6cf6fda scoped_refptr<>::~scoped_refptr()
#16 0x7f39f6cf6a95 base::internal::CallbackBase::~CallbackBase()
#17 0x0014b7b21005 base::internal::CallbackBaseCopyable::~CallbackBaseCopyable()
#18 0x0014b87b0c48 chrome::mojom::EmbeddedSearchStubDispatch::AcceptWithResponder()
#19 0x0014bcaf7b79 chrome::mojom::EmbeddedSearchStub<>::AcceptWithResponder()
#20 0x7f39f51d2622 mojo::InterfaceEndpointClient::HandleValidatedMessage()
#21 0x7f39f51d1c71 mojo::InterfaceEndpointClient::HandleIncomingMessageThunk::Accept()
#22 0x7f39f51d02ec mojo::FilterChain::Accept()
#23 0x7f39f51d5db1 mojo::InterfaceEndpointClient::HandleIncomingMessage()
#24 0x7f39f506c035 IPC::(anonymous namespace)::ChannelAssociatedGroupController::AcceptOnProxyThread()
#25 0x7f39f506320a _ZN4base8internal13FunctorTraitsIMN3IPC12_GLOBAL__N_132ChannelAssociatedGroupControllerEFvN4mojo7MessageEEvE6InvokeIRK13scoped_refptrIS4_EJS6_EEEvS8_OT_DpOT0_
#26 0x7f39f50630cf _ZN4base8internal12InvokeHelperILb0EvE8MakeItSoIRKMN3IPC12_GLOBAL__N_132ChannelAssociatedGroupControllerEFvN4mojo7MessageEEJRK13scoped_refptrIS6_ES8_EEEvOT_DpOT0_
#27 0x7f39f506303f _ZN4base8internal7InvokerINS0_9BindStateIMN3IPC12_GLOBAL__N_132ChannelAssociatedGroupControllerEFvN4mojo7MessageEEJ13scoped_refptrIS5_ENS0_13PassedWrapperIS7_EEEEEFvvEE7RunImplIRKS9_RKNSt3__15tupleIJSB_SD_EEEJLm0ELm1EEEEvOT_OT0_NSK_16integer_sequenceImJXspT1_EEEE
#28 0x7f39f5062efc _ZN4base8internal7InvokerINS0_9BindStateIMN3IPC12_GLOBAL__N_132ChannelAssociatedGroupControllerEFvN4mojo7MessageEEJ13scoped_refptrIS5_ENS0_13PassedWrapperIS7_EEEEEFvvEE3RunEPNS0_13BindStateBaseE
#29 0x7f39f6cf3f01 _ZNO4base12OnceCallbackIFvvEE3RunEv
#30 0x7f39f6d4905a base::debug::TaskAnnotator::RunTask()
#31 0x7f39f6de9275 base::internal::IncomingTaskQueue::RunTask()
#32 0x7f39f6dee2c4 base::MessageLoop::RunTask()
#33 0x7f39f6dee547 base::MessageLoop::DeferOrRunPendingTask()
#34 0x7f39f6def230 base::MessageLoop::DoWork()
#35 0x7f39f6df4d3c base::MessagePumpGlib::HandleDispatch()
#36 0x7f39f6df54e1 base::(anonymous namespace)::WorkSourceDispatch()
#37 0x7f39dfeefe04 g_main_context_dispatch
#38 0x7f39dfef0048 <unknown>
#39 0x7f39dfef00ec g_main_context_iteration
#40 0x7f39f6df4e3f base::MessagePumpGlib::Run()
#41 0x7f39f6deda84 base::MessageLoop::Run()
#42 0x7f39f6e9af05 base::RunLoop::Run()
#43 0x0014b913956d ChromeBrowserMainParts::MainMessageLoopRun()
#44 0x7f39f110be06 content::BrowserMainLoop::RunMainMessageLoopParts()
#45 0x7f39f1113b1f content::BrowserMainRunnerImpl::Run()
#46 0x7f39f10fff8b content::BrowserMain()
#47 0x7f39f2ac1db4 content::RunNamedProcessTypeMain()
#48 0x7f39f2ac497e content::ContentMainRunnerImpl::Run()
#49 0x7f39f2abf54d content::ContentServiceManagerMainDelegate::RunEmbedderProcess()
#50 0x7f39f75b77b5 service_manager::Main()
#51 0x7f39f2ac0c2f content::ContentMain()
#52 0x0014b7b1c22e ChromeMain
#53 0x0014b7b1c142 main
#54 0x7f39dd880f45 __libc_start_main
#55 0x0014b7b1c029 <unknown>