App Version: 67.0.3376.0 Canary
iOS Version: 11.3 beta 6, 10.3.3
Device: iPhone and iPad
URL: https://developer.apple.com/fonts/
https://www.barebones.com/products/bbedit/download.html

Steps to reproduce:
1. Launch chrome 
2. Load above URLS in separate tabs
3. Tap on download file in each tab page
4. Go to tab 2, perform pull to refresh to close the tab
5. Again pull to refresh in tab 1 and close the tab

Observed results:
App crashes

Note: If the tabs are closed from tab switcher the app will not crash

Expected results:
App shouldn’t crash

Number of times you were able to reproduce: 5/5
Bug reproducible after clean install: Yes
Bug reproducible after clearing cache and cookies: Yes
Bug reproducible on Chrome Mobile on Android: Not tested
Bug reproducible on Safari/Firefox: Firefox: NA, Safari: NA 
Bug reproducible on current stable build (App Version, iOS Version): No on M65 [New Download UI from M67]
Bug reproducible on the current beta channel build (App Version, iOS Version): No on M66 [New Download UI from M67]

Link to video/image:
https://drive.google.com/file/d/1qA5yiWJ9RYcmgmF1Hrp8Rpg5QwUvXAEF/view?usp=sharing

CRASH LOG:
https://crash.corp.google.com/browse?stbtiq=4c7d95143964bdfc#0

Stack trace:
Thread 0 (id: 771) CRASHED [EXC_SOFTWARE / UNCAUGHT_NS_EXCEPTION @ 0x0000000182ce7164 ] MAGIC SIGNATURE THREAD
Stack Quality84%Show frame trust levels
0x0000000182ce7164	(CoreFoundation + 0x00143164 )	__exceptionPreprocess
0x0000000181f30524	(libobjc.A.dylib + 0x00008524 )	objc_exception_throw
0x0000000182ce70a8	(CoreFoundation + 0x001430a8 )	+[NSException raise:format:]
0x00000001838018f0	(Foundation + 0x0022c8f0 )	-[NSLayoutConstraint _setActive:mutuallyExclusiveConstraints:]
0x0000000183801bdc	(Foundation + 0x0022cbdc )	__55+[NSLayoutConstraint _addOrRemoveConstraints:activate:]_block_invoke
0x00000001836234d8	(Foundation + 0x0004e4d8 )	-[NSISEngine withBehaviors:performModifications:]
0x0000000183801aac	(Foundation + 0x0022caac )	+[NSLayoutConstraint _addOrRemoveConstraints:activate:]
0x00000001033a1da0	(Chrome -vertical_animation_container.mm:105 )	__46-[VerticalAnimationContainer dismissAnimated:]_block_invoke
0x000000018c2d697c	(UIKit + 0x0004497c )	+[UIView(UIViewAnimationWithBlocks) _setupAnimationWithDuration:delay:view:options:factory:animations:start:animationStateGenerator:completion:]
0x000000018c40606c	(UIKit + 0x0017406c )	+[UIView(UIViewAnimationWithBlocks) animateWithDuration:animations:completion:]
0x00000001033a1c58	(Chrome -vertical_animation_container.mm:118 )	-[VerticalAnimationContainer dismissAnimated:]
0x0000000103391a78	(Chrome -download_manager_coordinator.mm:67 )	-[DownloadManagerCoordinator stop]
0x0000000102e5dc54	(Chrome -download_manager_tab_helper.mm:76 )	DownloadManagerTabHelper::WasHidden(web::WebState*)
0x0000000102dc57dc	(Chrome -web_state_impl.mm:593 )	web::WebStateImpl::WasHidden()
0x000000010336e3f0	(Chrome -browser_view_controller.mm:5055 )	-[BrowserViewController tabModel:didDeselectTab:]
0x0000000182ceeacc	(CoreFoundation + 0x0014aacc )	__invoking___
0x0000000182bcd368	(CoreFoundation + 0x00029368 )	-[NSInvocation invoke]
0x0000000182bd1e18	(CoreFoundation + 0x0002de18 )	-[NSInvocation invokeWithTarget:]
0x00000001035a4c90	(Chrome -crb_protocol_observers.mm:169 )	-[CRBProtocolObservers forwardInvocation:]
0x0000000182cec818	(CoreFoundation + 0x00148818 )	___forwarding___
0x0000000182bd1cc8	(CoreFoundation + 0x0002dcc8 )	_CF_forwarding_prep_0
0x00000001035150b0	(Chrome -tab_model.mm:603 )	-[TabModel notifyTabWasDeselected:]
0x0000000103519914	(Chrome -tab_model_selected_tab_observer.mm:43 )	-[TabModelSelectedTabObserver webStateList:didChangeActiveWebState:oldWebState:atIndex:reason:]
0x0000000102f2f6f4	(Chrome -web_state_list_observer_bridge.mm:117 )	WebStateListObserverBridge::WebStateActivatedAt(WebStateList*, web::WebState*, web::WebState*, int, int)
0x0000000102f2df20	(Chrome -web_state_list.mm:325 )	WebStateList::NotifyIfActiveWebStateChanged(web::WebState*, int)
0x0000000102f2e164	(Chrome -web_state_list.mm:269 )	WebStateList::DetachWebStateAt(int)
0x0000000102f2e244	(Chrome -web_state_list.mm:278 )	WebStateList::CloseWebStateAt(int, int)
0x000000010336ca60	(Chrome -browser_view_controller.mm:4748 )	-[BrowserViewController closeCurrentTab]
0x0000000103367b88	(Chrome -browser_view_controller.mm:3707 )	-[BrowserViewController overscrollActionsController:didTriggerAction:]
0x000000010304aaec	(Chrome -overscroll_actions_controller.mm:708 )	__52-[OverscrollActionsController triggerActionIfNeeded]_block_invoke
0x0000000182666a50	(libdispatch.dylib + 0x00001a50 )	_dispatch_call_block_and_release
0x0000000182666a10	(libdispatch.dylib + 0x00001a10 )	_dispatch_client_callout
0x00000001826a7c7c	(libdispatch.dylib + 0x00042c7c )	_dispatch_main_queue_callback_4CF$VARIANT$armv81
0x0000000182c8f340	(CoreFoundation + 0x000eb340 )	__CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__
0x0000000182c8cf1c	(CoreFoundation + 0x000e8f1c )	__CFRunLoopRun
0x0000000182bacc54	(CoreFoundation + 0x00008c54 )	CFRunLoopRunSpecific
0x0000000184a58f80	(GraphicsServices + 0x0000af80 )	GSEventRunModal
0x000000018c3055c0	(UIKit + 0x000735c0 )	UIApplicationMain
0x0000000102c30150	(Chrome -chrome_exe_main.mm:54 )	main
0x00000001826cc568	(libdyld.dylib + 0x00001568 )	start