Happened in https://ci.chromium.org/p/chromium/builders/luci.chromium.try/ios-simulator/38264 on unrelated CL.

[0627/114831.615532:FATAL:session_sync_bridge.cc(342)] Check failed: !syncing_.
0   ios_chrome_ui_egtests               0x000000010c0c59ad base::debug::StackTrace::StackTrace(unsigned long) + 157
1   ios_chrome_ui_egtests               0x000000010c0c59ed base::debug::StackTrace::StackTrace(unsigned long) + 29
2   ios_chrome_ui_egtests               0x000000010bdd659c base::debug::StackTrace::StackTrace() + 28
3   ios_chrome_ui_egtests               0x000000010be1caac logging::LogMessage::~LogMessage() + 460
4   ios_chrome_ui_egtests               0x000000010be1a915 logging::LogMessage::~LogMessage() + 21
5   ios_chrome_ui_egtests               0x000000010f887e97 sync_sessions::SessionSyncBridge::OnSyncStarting(syncer::DataTypeActivationRequest const&) + 199
6   ios_chrome_ui_egtests               0x000000010dfd6b95 syncer::ClientTagBasedModelTypeProcessor::OnSyncStarting(syncer::DataTypeActivationRequest const&, base::OnceCallback<void (std::__1::unique_ptr<syncer::DataTypeActivationResponse, std::__1::default_delete<syncer::DataTypeActivationResponse> >)>) + 981
7   ios_chrome_ui_egtests               0x000000010de5c70c syncer::(anonymous namespace)::OnSyncStartingHelperOnModelThread(syncer::DataTypeActivationRequest const&, base::OnceCallback<void (std::__1::unique_ptr<syncer::DataTypeActivationResponse, std::__1::default_delete<syncer::DataTypeActivationResponse> >)>, base::WeakPtr<syncer::ModelTypeControllerDelegate>) + 92
8   ios_chrome_ui_egtests               0x000000010de64e9a void base::internal::FunctorTraits<void (*)(syncer::DataTypeActivationRequest const&, base::OnceCallback<void (std::__1::unique_ptr<syncer::DataTypeActivationResponse, std::__1::default_delete<syncer::DataTypeActivationResponse> >)>, base::WeakPtr<syncer::ModelTypeControllerDelegate>), void>::Invoke<void (*)(syncer::DataTypeActivationRequest const&, base::OnceCallback<void (std::__1::unique_ptr<syncer::DataTypeActivationResponse, std::__1::default_delete<syncer::DataTypeActivationResponse> >)>, base::WeakPtr<syncer::ModelTypeControllerDelegate>), syncer::DataTypeActivationRequest, base::OnceCallback<void (std::__1::unique_ptr<syncer::DataTypeActivationResponse, std::__1::default_delete<syncer::DataTypeActivationResponse> >)>, base::WeakPtr<syncer::ModelTypeControllerDelegate> >(void (*&&)(syncer::DataTypeActivationRequest const&, base::OnceCallback<void (std::__1::unique_ptr<syncer::DataTypeActivationResponse, std::__1::default_delete<syncer::DataTypeActivationResponse> >)>, base::WeakPtr<syncer::ModelTypeControllerDelegate>), syncer::DataTypeActivationRequest&&, base::OnceCallback<void (std::__1::unique_ptr<syncer::DataTypeActivationResponse, std::__1::default_delete<syncer::DataTypeActivationResponse> >)>&&, base::WeakPtr<syncer::ModelTypeControllerDelegate>&&) + 122
9   ios_chrome_ui_egtests               0x000000010de64ddd void base::internal::InvokeHelper<false, void>::MakeItSo<void (*)(syncer::DataTypeActivationRequest const&, base::OnceCallback<void (std::__1::unique_ptr<syncer::DataTypeActivationResponse, std::__1::default_delete<syncer::DataTypeActivationResponse> >)>, base::WeakPtr<syncer::ModelTypeControllerDelegate>), syncer::DataTypeActivationRequest, base::OnceCallback<void (std::__1::unique_ptr<syncer::DataTypeActivationResponse, std::__1::default_delete<syncer::DataTypeActivationResponse> >)>, base::WeakPtr<syncer::ModelTypeControllerDelegate> >(void (*&&)(syncer::DataTypeActivationRequest const&, base::OnceCallback<void (std::__1::unique_ptr<syncer::DataTypeActivationResponse, std::__1::default_delete<syncer::DataTypeActivationResponse> >)>, base::WeakPtr<syncer::ModelTypeControllerDelegate>), syncer::DataTypeActivationRequest&&, base::OnceCallback<void (std::__1::unique_ptr<syncer::DataTypeActivationResponse, std::__1::default_delete<syncer::DataTypeActivationResponse> >)>&&, base::WeakPtr<syncer::ModelTypeControllerDelegate>&&) + 77
10  ios_chrome_ui_egtests               0x000000010de64d7d void base::internal::Invoker<base::internal::BindState<void (*)(syncer::DataTypeActivationRequest const&, base::OnceCallback<void (std::__1::unique_ptr<syncer::DataTypeActivationResponse, std::__1::default_delete<syncer::DataTypeActivationResponse> >)>, base::WeakPtr<syncer::ModelTypeControllerDelegate>), syncer::DataTypeActivationRequest, base::OnceCallback<void (std::__1::unique_ptr<syncer::DataTypeActivationResponse, std::__1::default_delete<syncer::DataTypeActivationResponse> >)> >, void (base::WeakPtr<syncer::ModelTypeControllerDelegate>)>::RunImpl<void (*)(syncer::DataTypeActivationRequest const&, base::OnceCallback<void (std::__1::unique_ptr<syncer::DataTypeActivationResponse, std::__1::default_delete<syncer::DataTypeActivationResponse> >)>, base::WeakPtr<syncer::ModelTypeControllerDelegate>), std::__1::tuple<syncer::DataTypeActivationRequest, base::OnceCallback<void (std::__1::unique_ptr<syncer::DataTypeActivationResponse, std::__1::default_delete<syncer::DataTypeActivationResponse> >)> >, 0ul, 1ul>(void (*&&)(syncer::DataTypeActivationRequest const&, base::OnceCallback<void (std::__1::unique_ptr<syncer::DataTypeActivationResponse, std::__1::default_delete<syncer::DataTypeActivationResponse> >)>, base::WeakPtr<syncer::ModelTypeControllerDelegate>), std::__1::tuple<syncer::DataTypeActivationRequest, base::OnceCallback<void (std::__1::unique_ptr<syncer::DataTypeActivationResponse, std::__1::default_delete<syncer::DataTypeActivationResponse> >)> >&&, std::__1::integer_sequence<unsigned long, 0ul, 1ul>, base::WeakPtr<syncer::ModelTypeControllerDelegate>&&) + 141
11  ios_chrome_ui_egtests               0x000000010de64c59 base::internal::Invoker<base::internal::BindState<void (*)(syncer::DataTypeActivationRequest const&, base::OnceCallback<void (std::__1::unique_ptr<syncer::DataTypeActivationResponse, std::__1::default_delete<syncer::DataTypeActivationResponse> >)>, base::WeakPtr<syncer::ModelTypeControllerDelegate>), syncer::DataTypeActivationRequest, base::OnceCallback<void (std::__1::unique_ptr<syncer::DataTypeActivationResponse, std::__1::default_delete<syncer::DataTypeActivationResponse> >)> >, void (base::WeakPtr<syncer::ModelTypeControllerDelegate>)>::RunOnce(base::internal::BindStateBase*, base::WeakPtr<syncer::ModelTypeControllerDelegate>&&) + 73
12  ios_chrome_ui_egtests               0x000000010de6141c base::OnceCallback<void (base::WeakPtr<syncer::ModelTypeControllerDelegate>)>::Run(base::WeakPtr<syncer::ModelTypeControllerDelegate>) + 108
13  ios_chrome_ui_egtests               0x000000010de6074b syncer::(anonymous namespace)::RunModelTask(base::OnceCallback<base::WeakPtr<syncer::ModelTypeControllerDelegate> ()>, base::OnceCallback<void (base::WeakPtr<syncer::ModelTypeControllerDelegate>)>) + 107
14  ios_chrome_ui_egtests               0x000000010de68b1f void base::internal::FunctorTraits<void (*)(base::OnceCallback<base::WeakPtr<syncer::ModelTypeControllerDelegate> ()>, base::OnceCallback<void (base::WeakPtr<syncer::ModelTypeControllerDelegate>)>), void>::Invoke<void (*)(base::OnceCallback<base::WeakPtr<syncer::ModelTypeControllerDelegate> ()>, base::OnceCallback<void (base::WeakPtr<syncer::ModelTypeControllerDelegate>)>), base::OnceCallback<base::WeakPtr<syncer::ModelTypeControllerDelegate> ()>, base::OnceCallback<void (base::WeakPtr<syncer::ModelTypeControllerDelegate>)> >(void (*&&)(base::OnceCallback<base::WeakPtr<syncer::ModelTypeControllerDelegate> ()>, base::OnceCallback<void (base::WeakPtr<syncer::ModelTypeControllerDelegate>)>), base::OnceCallback<base::WeakPtr<syncer::ModelTypeControllerDelegate> ()>&&, base::OnceCallback<void (base::WeakPtr<syncer::ModelTypeControllerDelegate>)>&&) + 95
15  ios_chrome_ui_egtests               0x000000010de68a4d void base::internal::InvokeHelper<false, void>::MakeItSo<void (*)(base::OnceCallback<base::WeakPtr<syncer::ModelTypeControllerDelegate> ()>, base::OnceCallback<void (base::WeakPtr<syncer::ModelTypeControllerDelegate>)>), base::OnceCallback<base::WeakPtr<syncer::ModelTypeControllerDelegate> ()>, base::OnceCallback<void (base::WeakPtr<syncer::ModelTypeControllerDelegate>)> >(void (*&&)(base::OnceCallback<base::WeakPtr<syncer::ModelTypeControllerDelegate> ()>, base::OnceCallback<void (base::WeakPtr<syncer::ModelTypeControllerDelegate>)>), base::OnceCallback<base::WeakPtr<syncer::ModelTypeControllerDelegate> ()>&&, base::OnceCallback<void (base::WeakPtr<syncer::ModelTypeControllerDelegate>)>&&) + 61
16  ios_chrome_ui_egtests               0x000000010de689fd void base::internal::Invoker<base::internal::BindState<void (*)(base::OnceCallback<base::WeakPtr<syncer::ModelTypeControllerDelegate> ()>, base::OnceCallback<void (base::WeakPtr<syncer::ModelTypeControllerDelegate>)>), base::OnceCallback<base::WeakPtr<syncer::ModelTypeControllerDelegate> ()>, base::OnceCallback<void (base::WeakPtr<syncer::ModelTypeControllerDelegate>)> >, void ()>::RunImpl<void (*)(base::OnceCallback<base::WeakPtr<syncer::ModelTypeControllerDelegate> ()>, base::OnceCallback<void (base::WeakPtr<syncer::ModelTypeControllerDelegate>)>), std::__1::tuple<base::OnceCallback<base::WeakPtr<syncer::ModelTypeControllerDelegate> ()>, base::OnceCallback<void (base::WeakPtr<syncer::ModelTypeControllerDelegate>)> >, 0ul, 1ul>(void (*&&)(base::OnceCallback<base::WeakPtr<syncer::ModelTypeControllerDelegate> ()>, base::OnceCallback<void (base::WeakPtr<syncer::ModelTypeControllerDelegate>)>), std::__1::tuple<base::OnceCallback<base::WeakPtr<syncer::ModelTypeControllerDelegate> ()>, base::OnceCallback<void (base::WeakPtr<syncer::ModelTypeControllerDelegate>)> >&&, std::__1::integer_sequence<unsigned long, 0ul, 1ul>) + 125
17  ios_chrome_ui_egtests               0x000000010de68919 base::internal::Invoker<base::internal::BindState<void (*)(base::OnceCallback<base::WeakPtr<syncer::ModelTypeControllerDelegate> ()>, base::OnceCallback<void (base::WeakPtr<syncer::ModelTypeControllerDelegate>)>), base::OnceCallback<base::WeakPtr<syncer::ModelTypeControllerDelegate> ()>, base::OnceCallback<void (base::WeakPtr<syncer::ModelTypeControllerDelegate>)> >, void ()>::RunOnce(base::internal::BindStateBase*) + 57
18  ios_chrome_ui_egtests               0x0000000109e67ffe base::OnceCallback<void ()>::Run() && + 78
19  ios_chrome_ui_egtests               0x000000010bdd78b3 base::debug::TaskAnnotator::RunTask(char const*, base::PendingTask*) + 979
20  ios_chrome_ui_egtests               0x000000010be4104a base::internal::IncomingTaskQueue::RunTask(base::PendingTask*) + 234
21  ios_chrome_ui_egtests               0x000000010be4d2d8 base::MessageLoop::RunTask(base::PendingTask*) + 872
22  ios_chrome_ui_egtests               0x000000010be4d889 base::MessageLoop::DeferOrRunPendingTask(base::PendingTask) + 89
23  ios_chrome_ui_egtests               0x000000010be4dbda base::MessageLoop::DoWork() + 570
24  ios_chrome_ui_egtests               0x000000010c0f4224 base::MessagePumpCFRunLoopBase::RunWork() + 84
25  ios_chrome_ui_egtests               0x000000010c0f41bc ___ZN4base24MessagePumpCFRunLoopBase13RunWorkSourceEPv_block_invoke + 28
26  ios_chrome_ui_egtests               0x000000010c0e6af1 base::mac::CallWithEHFrame(void () block_pointer) + 33
27  ios_chrome_ui_egtests               0x000000010c0f3467 base::MessagePumpCFRunLoopBase::RunWorkSource(void*) + 87
28  CoreFoundation                      0x000000011898a101 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
29  CoreFoundation                      0x0000000118a29f71 __CFRunLoopDoSource0 + 81
30  CoreFoundation                      0x000000011896ea19 __CFRunLoopDoSources0 + 185
31  CoreFoundation                      0x000000011896dfff __CFRunLoopRun + 1279
32  CoreFoundation                      0x000000011896d889 CFRunLoopRunSpecific + 409
33  EarlGrey                            0x000000011a8d6b0e -[GREYRunLoopSpinner grey_drainRunLoopInActiveModeAndCheckCondition:forTime:] + 590
34  EarlGrey                            0x000000011a8d6535 -[GREYRunLoopSpinner spinWithStopConditionBlock:] + 421
35  EarlGrey                            0x000000011a8bcaed -[GREYTouchInjector waitUntilAllTouchesAreDeliveredUsingInjector] + 493
36  EarlGrey                            0x000000011a8bc154 -[GREYSyntheticEvents grey_endTouchesAtPoints:timeElapsedSinceLastTouchDelivery:] + 180
37  EarlGrey                            0x000000011a8bb2f6 +[GREYSyntheticEvents touchAlongMultiplePaths:relativeToWindow:forDuration:expendable:] + 934
38  EarlGrey                            0x000000011a8baeed +[GREYSyntheticEvents touchAlongPath:relativeToWindow:forDuration:expendable:] + 221
39  EarlGrey                            0x000000011a87daf4 +[GREYTapper tapOnWindow:numberOfTaps:location:error:] + 404
40  EarlGrey                            0x000000011a87d90b +[GREYTapper tapOnElement:numberOfTaps:location:error:] + 827
41  EarlGrey                            0x000000011a87cc03 -[GREYTapAction perform:error:] + 371
42  EarlGrey                            0x000000011a8ad5ae __46-[GREYElementInteraction performAction:error:]_block_invoke + 958
43  EarlGrey                            0x000000011a8da2b4 __59-[GREYUIThreadExecutor executeSyncWithTimeout:block:error:]_block_invoke + 68
44  EarlGrey                            0x000000011a8d6eec __77-[GREYRunLoopSpinner grey_drainRunLoopInActiveModeAndCheckCondition:forTime:]_block_invoke + 316
45  EarlGrey                            0x000000011a8d7abf __89-[GREYRunLoopSpinner grey_setupObserverInMode:withBeforeSourcesBlock:beforeWaitingBlock:]_block_invoke + 175
46  CoreFoundation                      0x0000000118989c07 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23
47  CoreFoundation                      0x0000000118989b5e __CFRunLoopDoObservers + 430
48  CoreFoundation                      0x000000011896dfe3 __CFRunLoopRun + 1251
49  CoreFoundation                      0x000000011896d889 CFRunLoopRunSpecific + 409
50  EarlGrey                            0x000000011a8d6b0e -[GREYRunLoopSpinner grey_drainRunLoopInActiveModeAndCheckCondition:forTime:] + 590
51  EarlGrey                            0x000000011a8d6535 -[GREYRunLoopSpinner spinWithStopConditionBlock:] + 421
52  EarlGrey                            0x000000011a8d9d1e -[GREYUIThreadExecutor executeSyncWithTimeout:block:error:] + 1006
53  EarlGrey                            0x000000011a8ac84f -[GREYElementInteraction performAction:error:] + 1791
54  EarlGrey                            0x000000011a8ac11f -[GREYElementInteraction performAction:] + 79
55  ios_chrome_ui_egtests               0x000000010bc40924 +[ChromeEarlGreyUI confirmSigninConfirmationDialog] + 1204
56  ios_chrome_ui_egtests               0x000000010bd51ef0 -[SigninInteractionControllerTestCase testSignInSwitchAccountsAndKeepDataSeparate] + 384
57  CoreFoundation                      0x000000011896b36c __invoking___ + 140
58  CoreFoundation                      0x000000011896b240 -[NSInvocation invoke] + 320
59  EarlGrey                            0x000000011a8a23e8 -[GREYTestCaseInvocation invoke] + 104
60  XCTest                              0x0000000119db1e30 __24-[XCTestCase invokeTest]_block_invoke + 591
61  XCTest                              0x0000000119dfb17e -[XCUITestContext performInScope:] + 183