Chrome Version: 68.0.3436.0 (Official Build) canary (64-bit) (cohort: Clang-64)
OS: Windows 10 1803 (OS Build 17134.48)

What steps will reproduce the problem?
(1) Run chrome as normal
(2) Launch chrome from another application, or a second shortcut
(3)

What is the expected result?

Chrome launches a new window, should rendez-vous with current Chrome, fire new window, then self-terminate.

What happens instead?

Popup "Google Chrome is unresponsive. Relaunch now?"
chrome browser process child that is launched uses an entire core.

the main thread of the second chrome (the one displaying the dialog) is:

0:000> kn
 # Child-SP          RetAddr           Call Site
00 000000ae`549fd698 00007ff9`f5d99bfc win32u!NtUserWaitMessage+0x14
01 000000ae`549fd6a0 00007ff9`f5d999de user32!DialogBox2+0x1fc
02 000000ae`549fd730 00007ff9`f5ddf660 user32!InternalDialogBox+0x11e
03 000000ae`549fd790 00007ff9`f5dde0b5 user32!SoftModalMessageBox+0x7f0
04 000000ae`549fd8e0 00007ff9`f5ddedd2 user32!MessageBoxWorker+0x2f9
05 000000ae`549fda90 00007ff9`f5ddee5e user32!MessageBoxTimeoutW+0x192
06 000000ae`549fdb90 00007ff9`bb71fe67 user32!MessageBoxW+0x4e
07 000000ae`549fdbd0 00007ff9`bc06c466 chrome!ui::MessageBoxW+0xb3 [C:\b\c\b\win64_clang\src\ui\base\win\message_box_win.cc @ 30] 
08 000000ae`549fdc90 00007ff9`bc06c338 chrome!SimpleMessageBoxViews::Show+0x276 [C:\b\c\b\win64_clang\src\chrome\browser\ui\views\simple_message_box_views.cc @ 116] 
09 (Inline Function) --------`-------- chrome!`anonymous namespace'::ShowSync+0xb1 [C:\b\c\b\win64_clang\src\chrome\browser\ui\views\simple_message_box_views.cc @ 68] 
0a 000000ae`549fde50 00007ff9`bc06cbe6 chrome!SimpleMessageBoxViews::Show+0x148 [C:\b\c\b\win64_clang\src\chrome\browser\ui\views\simple_message_box_views.cc @ 97] 
0b 000000ae`549fe010 00007ff9`bc1ca2ab chrome!chrome::ShowQuestionMessageBox+0x83 [C:\b\c\b\win64_clang\src\chrome\browser\ui\views\simple_message_box_views.cc @ 310] 
0c 000000ae`549fe0f0 00007ff9`ba16120e chrome!`anonymous namespace'::DisplayShouldKillMessageBox+0x47 [C:\b\c\b\win64_clang\src\chrome\browser\process_singleton_win.cc @ 177] 
0d (Inline Function) --------`-------- chrome!base::RepeatingCallback<bool ()>::Run+0x7 [C:\b\c\b\win64_clang\src\base\callback.h @ 125] 
0e 000000ae`549fe180 00007ff9`ba1603b2 chrome!ProcessSingleton::NotifyOtherProcess+0xe2 [C:\b\c\b\win64_clang\src\chrome\browser\process_singleton_win.cc @ 319] 
0f 000000ae`549fe240 00007ff9`ba15182a chrome!ProcessSingleton::NotifyOtherProcessOrCreate+0x46 [C:\b\c\b\win64_clang\src\chrome\browser\process_singleton_win.cc @ 344] 
10 000000ae`549fe300 00007ff9`ba1513be chrome!ChromeBrowserMainParts::PreMainMessageLoopRunImpl+0x366 [C:\b\c\b\win64_clang\src\chrome\browser\chrome_browser_main.cc @ 1666] 
11 000000ae`549fe670 00007ff9`ba151233 chrome!ChromeBrowserMainParts::PreMainMessageLoopRun+0xb6 [C:\b\c\b\win64_clang\src\chrome\browser\chrome_browser_main.cc @ 1469] 
12 000000ae`549fe750 00007ff9`ba0a275c chrome!content::BrowserMainLoop::PreMainMessageLoopRun+0x55 [C:\b\c\b\win64_clang\src\content\browser\browser_main_loop.cc @ 953] 
13 (Inline Function) --------`-------- chrome!base::RepeatingCallback<int ()>::Run+0x7 [C:\b\c\b\win64_clang\src\base\callback.h @ 125] 
14 000000ae`549fe830 00007ff9`ba0a24ea chrome!content::StartupTaskRunner::RunAllTasksNow+0x1c [C:\b\c\b\win64_clang\src\content\browser\startup_task_runner.cc @ 44] 
15 000000ae`549fe870 00007ff9`ba047fa0 chrome!content::BrowserMainLoop::CreateStartupTasks+0x2e0 [C:\b\c\b\win64_clang\src\content\browser\browser_main_loop.cc @ 868] 
16 000000ae`549fe9b0 00007ff9`ba047ce4 chrome!content::BrowserMainRunnerImpl::Initialize+0x7e [C:\b\c\b\win64_clang\src\content\browser\browser_main_runner_impl.cc @ 140] 
17 000000ae`549feb20 00007ff9`ba047b97 chrome!content::BrowserMain+0xb0 [C:\b\c\b\win64_clang\src\content\browser\browser_main.cc @ 42] 
18 000000ae`549fec00 00007ff9`ba047a41 chrome!content::RunNamedProcessTypeMain+0x11a [C:\b\c\b\win64_clang\src\content\app\content_main_runner_impl.cc @ 640] 
19 000000ae`549fed60 00007ff9`ba03502b chrome!content::ContentMainRunnerImpl::Run+0x115 [C:\b\c\b\win64_clang\src\content\app\content_main_runner_impl.cc @ 946] 
1a 000000ae`549fee00 00007ff9`ba034af8 chrome!service_manager::Main+0x46e [C:\b\c\b\win64_clang\src\services\service_manager\embedder\main.cc @ 452] 
1b 000000ae`549ff130 00007ff9`ba031b92 chrome!content::ContentMain+0x41 [C:\b\c\b\win64_clang\src\content\app\content_main.cc @ 19] 
1c 000000ae`549ff1c0 00007ff7`a99936ec chrome!ChromeMain+0x120 [C:\b\c\b\win64_clang\src\chrome\app\chrome_main.cc @ 104] 
1d 000000ae`549ff2a0 00007ff7`a9991699 chrome_exe!MainDllLoader::Launch+0x26c [C:\b\c\b\win64_clang\src\chrome\app\main_dll_loader_win.cc @ 201] 
1e 000000ae`549ff390 00007ff7`a9a6e222 chrome_exe!wWinMain+0x699 [C:\b\c\b\win64_clang\src\chrome\app\chrome_exe_main_win.cc @ 230] 
1f (Inline Function) --------`-------- chrome_exe!invoke_main+0x21 [f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl @ 118] 
20 000000ae`549ff770 00007ff9`f59d3034 chrome_exe!__scrt_common_main_seh+0x106 [f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl @ 283] 
21 000000ae`549ff7b0 00007ff9`f8061551 kernel32!BaseThreadInitThunk+0x14
22 000000ae`549ff7e0 00000000`00000000 ntdll!RtlUserThreadStart+0x21


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