I hit this assert in closing the last tab of a debug Chromium build.

Chromium	60.0.3098.0 (Developer Build) (32-bit) 
Revision	11ff05ed553a9e11a1fbe6eadc8d8b280c67a3d9-
OS	Windows
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Fatal error
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[23700:12532:0517/171836.466:FATAL:important_file_writer.cc(164)] Check failed: !HasPendingWrite(). 
Backtrace:
	base::debug::StackTrace::StackTrace [0x100AD4D7+55]
	base::debug::StackTrace::StackTrace [0x100AD171+17]
	logging::LogMessage::~LogMessage [0x10100ECE+94]
	base::ImportantFileWriter::~ImportantFileWriter [0x100EE4FB+123]
	JsonPrefStore::~JsonPrefStore [0x0CEF9AF2+130]
	JsonPrefStore::`vector deleting destructor' [0x0469E0C0+16]
	base::RefCounted<PrefStore>::Release [0x0CEECC62+82]
	scoped_refptr<PersistentPrefStore>::Release [0x03888FEF+15]
	scoped_refptr<PersistentPrefStore>::~scoped_refptr<PersistentPrefStore> [0x0388769A+26]
	SegregatedPrefStore::~SegregatedPrefStore [0x046DD158+152]
	SegregatedPrefStore::`vector deleting destructor' [0x046DD1EF+15]
	base::RefCounted<PrefStore>::Release [0x0CEECC62+82]
	scoped_refptr<PersistentPrefStore>::Release [0x0CF024CE+14]
	scoped_refptr<PersistentPrefStore>::operator= [0x0CF23F7A+58]
	PrefService::~PrefService [0x0CF23D6F+175]
	sync_preferences::PrefServiceSyncable::~PrefServiceSyncable [0x060CFDE9+105]
	sync_preferences::PrefServiceSyncable::`vector deleting destructor' [0x060D07DF+15]
	std::default_delete<sync_preferences::PrefServiceSyncable>::operator() [0x0695A9B9+41]
	std::unique_ptr<sync_preferences::PrefServiceSyncable,std::default_delete<sync_preferences::PrefServiceSyncable> >::~unique_ptr<sync_preferences::PrefServiceSyncable,std::default_delete<sync_preferences::PrefServiceSyncable> > [0x0695A5FB+43]
	ProfileImpl::~ProfileImpl [0x06A6D918+408]
	ProfileImpl::`vector deleting destructor' [0x06A6ED6F+15]
	ProfileDestroyer::DestroyProfileWhenAppropriate [0x06A4B7F7+679]
	ProfileManager::ProfileInfo::~ProfileInfo [0x068A26A5+21]
	ProfileManager::ProfileInfo::`scalar deleting destructor' [0x068A405F+15]
	linked_ptr<ProfileManager::ProfileInfo>::depart [0x068B0CA9+57]
	linked_ptr<ProfileManager::ProfileInfo>::~linked_ptr<ProfileManager::ProfileInfo> [0x068A232F+15]
	std::pair<base::FilePath const ,linked_ptr<ProfileManager::ProfileInfo> >::~pair<base::FilePath const ,linked_ptr<ProfileManager::ProfileInfo> > [0x068A2372+18]
	std::pair<base::FilePath const ,linked_ptr<ProfileManager::ProfileInfo> >::`scalar deleting destructor' [0x068A3F9F+15]
	std::allocator<std::_Tree_node<std::pair<base::FilePath const ,linked_ptr<ProfileManager::ProfileInfo> >,void *> >::destroy<std::pair<base::FilePath const ,linked_ptr<ProfileManager::ProfileInfo> > > [0x068A07C1+17]
	std::allocator_traits<std::allocator<std::_Tree_node<std::pair<base::FilePath const ,linked_ptr<ProfileManager::ProfileInfo> >,void *> > >::destroy<std::pair<base::FilePath const ,linked_ptr<ProfileManager::ProfileInfo> > > [0x068A07DF+15]
	std::_Wrap_alloc<std::allocator<std::_Tree_node<std::pair<base::FilePath const ,linked_ptr<ProfileManager::ProfileInfo> >,void *> > >::destroy<std::pair<base::FilePath const ,linked_ptr<ProfileManager::ProfileInfo> > > [0x068A0794+20]
	std::_Tree<std::_Tmap_traits<base::FilePath,linked_ptr<ProfileManager::ProfileInfo>,std::less<base::FilePath>,std::allocator<std::pair<base::FilePath const ,linked_ptr<ProfileManager::ProfileInfo> > >,0> >::_Erase [0x068AE707+119]
	std::_Tree<std::_Tmap_traits<base::FilePath,linked_ptr<ProfileManager::ProfileInfo>,std::less<base::FilePath>,std::allocator<std::pair<base::FilePath const ,linked_ptr<ProfileManager::ProfileInfo> > >,0> >::clear [0x068B0A35+37]
	std::_Tree<std::_Tmap_traits<base::FilePath,linked_ptr<ProfileManager::ProfileInfo>,std::less<base::FilePath>,std::allocator<std::pair<base::FilePath const ,linked_ptr<ProfileManager::ProfileInfo> > >,0> >::erase [0x068B0E9E+158]
	std::_Tree<std::_Tmap_traits<base::FilePath,linked_ptr<ProfileManager::ProfileInfo>,std::less<base::FilePath>,std::allocator<std::pair<base::FilePath const ,linked_ptr<ProfileManager::ProfileInfo> > >,0> >::_Tidy [0x068B0663+67]
	std::_Tree<std::_Tmap_traits<base::FilePath,linked_ptr<ProfileManager::ProfileInfo>,std::less<base::FilePath>,std::allocator<std::pair<base::FilePath const ,linked_ptr<ProfileManager::ProfileInfo> > >,0> >::~_Tree<std::_Tmap_traits<base::FilePath,linked_p [0x068A214F+15]
	std::map<base::FilePath,linked_ptr<ProfileManager::ProfileInfo>,std::less<base::FilePath>,std::allocator<std::pair<base::FilePath const ,linked_ptr<ProfileManager::ProfileInfo> > > >::~map<base::FilePath,linked_ptr<ProfileManager::ProfileInfo>,std::less<b [0x068A234F+15]
	ProfileManager::~ProfileManager [0x068A2719+73]
	ProfileManager::`vector deleting destructor' [0x068A409F+15]
	std::default_delete<ProfileManager>::operator() [0x04D4C9CA+42]
	std::unique_ptr<ProfileManager,std::default_delete<ProfileManager> >::reset [0x04D5646A+58]
	BrowserProcessImpl::StartTearDown [0x04D512CC+636]
	ChromeBrowserMainParts::PostMainMessageLoopRun [0x04CB43FE+478]
	content::BrowserMainLoop::ShutdownThreadsAndCleanUp [0x11AEDF41+561]
	content::BrowserMainRunnerImpl::Shutdown [0x11AF4160+1168]
	content::BrowserMain [0x11ADF686+182]
	content::RunNamedProcessTypeMain [0x135665D7+135]
	content::ContentMainRunnerImpl::Run [0x1356647C+572]
	content::ContentServiceManagerMainDelegate::RunEmbedderProcess [0x13564254+36]
	service_manager::Main [0x010BD739+777]
	content::ContentMain [0x13564749+41]
	ChromeMain [0x037239D0+256]
	MainDllLoader::Launch [0x0042F5FD+829]
	wWinMain [0x0042A4B0+576]
	invoke_main [0x004EA65E+30] (f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl:118)
	__scrt_common_main_seh [0x004EA4C0+336] (f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl:253)
	__scrt_common_main [0x004EA35D+13] (f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl:296)
	wWinMainCRTStartup [0x004EA678+8] (f:\dd\vctools\crt\vcstartup\src\startup\exe_wwinmain.cpp:17)
	BaseThreadInitThunk [0x758438F4+36]
	RtlUnicodeStringToInteger [0x77C15DE3+595]
	RtlUnicodeStringToInteger [0x77C15DAE+542]


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OK   
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