On top of tree Chromium, I opened the task manaager, opened 4 tabs (NTPs), and started closing them.

"""
[75038:1295:0601/110018:FATAL:task_manager.cc(941)] Check failed: process. 
0   Chromium Framework                  0x000000010b985f21 _ZN4base5debug10StackTraceC1Ev + 33
1   Chromium Framework                  0x000000010b9ac587 _ZN7logging10LogMessageD2Ev + 71
2   Chromium Framework                  0x0000000104d7b18f _ZN16TaskManagerModel11AddResourceEPN12task_manager8ResourceE + 127
3   Chromium Framework                  0x0000000104d83164 _ZN12task_manager27TaskManagerWebContentsEntry22CreateResourceForFrameEPN7content15RenderFrameHostE + 996
4   Chromium Framework                  0x000000010728a096 _ZN7content15WebContentsImpl18NotifyFrameSwappedEPNS_15RenderFrameHostES2_ + 342
5   Chromium Framework                  0x0000000106f15073 _ZN7content22RenderFrameHostManager13CommitPendingEv + 1011
6   Chromium Framework                  0x0000000106f136bd _ZN7content22RenderFrameHostManager22UpdateStateForNavigateERK4GURLPNS_12SiteInstanceES5_N2ui14PageTransitionEbbRKNS_15GlobalRequestIDEib + 1101
7   Chromium Framework                  0x0000000106f12db9 _ZN7content22RenderFrameHostManager8NavigateERK4GURLRKNS_20FrameNavigationEntryERKNS_19NavigationEntryImplEb + 249
8   Chromium Framework                  0x0000000106ef848b _ZN7content13NavigatorImpl15NavigateToEntryEPNS_13FrameTreeNodeERKNS_20FrameNavigationEntryERKNS_19NavigationEntryImplENS_20NavigationController10ReloadTypeEbb + 1291
9   Chromium Framework                  0x0000000106ef8dba _ZN7content13NavigatorImpl22NavigateToPendingEntryEPNS_13FrameTreeNodeERKNS_20FrameNavigationEntryENS_20NavigationController10ReloadTypeEb + 90
10  Chromium Framework                  0x0000000106ee9b63 _ZN7content24NavigationControllerImpl30NavigateToPendingEntryInternalENS_20NavigationController10ReloadTypeE + 355
11  Chromium Framework                  0x0000000106ee4bde _ZN7content24NavigationControllerImpl22NavigateToPendingEntryENS_20NavigationController10ReloadTypeE + 366
12  Chromium Framework                  0x0000000106ee666c _ZN7content24NavigationControllerImpl17LoadURLWithParamsERKNS_20NavigationController13LoadURLParamsE + 1756
13  Chromium Framework                  0x0000000108fc098f _ZN12_GLOBAL__N_117LoadURLInContentsEPN7content11WebContentsERK4GURLPN6chrome14NavigateParamsE + 383
14  Chromium Framework                  0x0000000108fc04e4 _ZN6chrome8NavigateEPNS_14NavigateParamsE + 2996
15  Chromium Framework                  0x0000000108fb7fe2 _ZN6chrome14OpenCurrentURLEP7Browser + 242
16  Chromium Framework                  0x0000000108fb593b _ZN6chrome24BrowserCommandController29ExecuteCommandWithDispositionEi21WindowOpenDisposition + 1947
17  Chromium Framework                  0x0000000104a564d1 _ZN14CommandUpdater29ExecuteCommandWithDispositionEi21WindowOpenDisposition + 257
18  Chromium Framework                  0x000000010948757b _ZN16OmniboxEditModel9OpenMatchE17AutocompleteMatch21WindowOpenDispositionRK4GURLRKNSt3__112basic_stringItN4base20string16_char_traitsENS5_9allocatorItEEEEm + 3851
19  Chromium Framework                  0x000000010949091e _ZN11OmniboxView9OpenMatchERK17AutocompleteMatch21WindowOpenDispositionRK4GURLRKNSt3__112basic_stringItN4base20string16_char_traitsENS7_9allocatorItEEEEm + 126
20  Chromium Framework                  0x000000010926d02b _ZN14OmniboxViewMac9OpenMatchERK17AutocompleteMatch21WindowOpenDispositionRK4GURLRKNSt3__112basic_stringItN4base20string16_char_traitsENS7_9allocatorItEEEEm + 43
21  Chromium Framework                  0x0000000109486629 _ZN16OmniboxEditModel11AcceptInputE21WindowOpenDispositionb + 1161
22  Chromium Framework                  0x000000010926fbdc _ZN14OmniboxViewMac21OnDoCommandBySelectorEP13objc_selector + 684
23  Chromium Framework                  0x0000000109252514 -[AutocompleteTextFieldEditor doCommandBySelector:] + 68
24  AppKit                              0x00007fff9a79771a -[NSTextInputContext(NSInputContext_WithCompletion) doCommandBySelector:completionHandler:] + 118
25  AppKit                              0x00007fff9a7733b9 -[NSKeyBindingManager(NSKeyBindingManager_MultiClients) interpretEventAsCommand:forClient:] + 1867
26  AppKit                              0x00007fff9a77ca3f __61-[NSTextInputContext _handleEvent:options:completionHandler:]_block_invoke978 + 335
27  AppKit                              0x00007fff9a7975da __61-[NSTextInputContext _handleEvent:options:completionHandler:]_block_invoke_3 + 95
28  AppKit                              0x00007fff9a77c8b1 -[NSTextInputContext tryHandleEvent_HasMarkedText_withDispatchCondition:dispatchWork:continuation:] + 101
29  AppKit                              0x00007fff9a77c83b __61-[NSTextInputContext _handleEvent:options:completionHandler:]_block_invoke966 + 321
30  HIToolbox                           0x00007fff86eb0bb8 __TSMProcessRawKeyEventWithOptionsAndCompletionHandler_block_invoke_5 + 70
31  HIToolbox                           0x00007fff86eafb41 ___ZL23DispatchEventToHandlersP14EventTargetRecP14OpaqueEventRefP14HandlerCallRec_block_invoke + 108
32  AppKit                              0x00007fff9a775bec __55-[NSTextInputContext handleTSMEvent:completionHandler:]_block_invoke176 + 2866
33  AppKit                              0x00007fff9a774fcc __55-[NSTextInputContext handleTSMEvent:completionHandler:]_block_invoke_2 + 95
34  AppKit                              0x00007fff9a774f3f -[NSTextInputContext tryHandleTSMEvent_HasMarkedText_withDispatchCondition:dispatchWork:continuation:] + 101
35  AppKit                              0x00007fff9a774c2f -[NSTextInputContext handleTSMEvent:completionHandler:] + 3173
36  AppKit                              0x00007fff9a773f5e _NSTSMEventHandler + 324
37  HIToolbox                           0x00007fff86e587be _ZL23DispatchEventToHandlersP14EventTargetRecP14OpaqueEventRefP14HandlerCallRec + 1231
38  HIToolbox                           0x00007fff86e57c48 _ZL30SendEventToEventTargetInternalP14OpaqueEventRefP20OpaqueEventTargetRefP14HandlerCallRec + 404
39  HIToolbox                           0x00007fff86e57aab SendEventToEventTargetWithOptions + 43
40  HIToolbox                           0x00007fff86eacf7d SendTSMEvent_WithCompletionHandler + 417
41  HIToolbox                           0x00007fff86ead46c __SendUnicodeTextAEToUnicodeDoc_WithCompletionHandler_block_invoke + 400
42  HIToolbox                           0x00007fff86ead2bf __SendFilterTextEvent_WithCompletionHandler_block_invoke + 189
43  HIToolbox                           0x00007fff86eacfcd SendTSMEvent_WithCompletionHandler + 497
44  HIToolbox                           0x00007fff86eacdaf SendFilterTextEvent_WithCompletionHandler + 236
45  HIToolbox                           0x00007fff86eaca88 SendUnicodeTextAEToUnicodeDoc_WithCompletionHandler + 284
46  HIToolbox                           0x00007fff86eac838 __utDeliverTSMEvent_WithCompletionHandler_block_invoke_2 + 296
47  HIToolbox                           0x00007fff86eac6dc __utDeliverTSMEvent_WithCompletionHandler_block_invoke + 437
48  HIToolbox                           0x00007fff86eac4cf TSMKeyEvent_WithCompletionHandler + 721
49  HIToolbox                           0x00007fff86eac1c5 __TSMProcessRawKeyEventWithOptionsAndCompletionHandler_block_invoke_4 + 251
50  HIToolbox                           0x00007fff86eac033 __TSMProcessRawKeyEventWithOptionsAndCompletionHandler_block_invoke_3 + 325
51  HIToolbox                           0x00007fff86eabd71 __TSMProcessRawKeyEventWithOptionsAndCompletionHandler_block_invoke_2 + 261
52  HIToolbox                           0x00007fff86eabb3a __TSMProcessRawKeyEventWithOptionsAndCompletionHandler_block_invoke + 253
53  HIToolbox                           0x00007fff86eab1f0 TSMProcessRawKeyEventWithOptionsAndCompletionHandler + 3199
54  AppKit                              0x00007fff9a773e0f __61-[NSTextInputContext _handleEvent:options:completionHandler:]_block_invoke955 + 131
55  AppKit                              0x00007fff9a772af1 -[NSTextInputContext tryTSMProcessRawKeyEvent:dispatchCondition:setupForDispatch:furtherCondition:dispatchWork:continuation:] + 131
56  AppKit                              0x00007fff9a7727eb -[NSTextInputContext _handleEvent:options:completionHandler:] + 1266
57  AppKit                              0x00007fff9a7722be -[NSTextInputContext handleEvent:] + 109
58  AppKit                              0x00007fff9a7721c7 -[NSView interpretKeyEvents:] + 204
59  Chromium Framework                  0x0000000109252294 -[AutocompleteTextFieldEditor interpretKeyEvents:] + 212
60  AppKit                              0x00007fff9a771ff2 -[NSTextView keyDown:] + 658
61  AppKit                              0x00007fff9ad9bbb5 -[NSWindow _reallySendEvent:isDelayedEvent:] + 2108
"""