Thanks for filing the issue!

Tried testing the issue on reported chrome version 69.0.3497.81 using Windows 7 with the below mentioned steps.
1. Launched Chrome
2. Navigated to https://remenku.pipipan.com/fs/2946809-308205513
3. Clicked on first blue button(with a downloading icon)
Observed a new page being opened with the downloading status of the file in the downloading bar(As shown in "881670 downloading status.png").

@Reporter: Could you please mention/clarify on "File downloading Dialog box pop up." mean the pop-up which looks like the one shown in attachment "881670 Pop-up". It would be highly helpful if elaborated on "blocking whole browser" as we are not very sure about the exact issue being faced by you. Any further inputs from your end may be helpful.

Deleted: 881670 downloading status.png 4.2 KB

	881670 downloading status.png 4.2 KB View Download

Deleted: 881670 Pop-up.png 276 KB

	881670 Pop-up.png 276 KB View Download

Thank you for providing more feedback. Adding the requester to the cc list.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Yes, your understanding is correct. "blocking whole browser" means when the dialog box(just like the second picture shown in attachment) didn't pop up, chrome was not responding to any mouse clicks. I can not reproduct the problem everytime. It sometimes appears and sometimes not(everything is back to normal), it's really strange.

I have recorded four short videos[1] of my steps to reproduce the problem. what's worse, not only downloading but also uploading file dialog box does not work. Drag and Drop File Uploading in Google Image Search and Google Drive also does not work. As you see in the videos, the dialog box does not pop up, chrome is not responding to any mouse clicks and i have to kill 'chrome.exe' process to restart chrome again.
 
[1]https://drive.google.com/file/d/1q53rh7kuER2SHQy4zdB9k_VHeaCIm6fR/view?usp=sharing

[Update],
I tried chrome beta, chrome 70 dev and reinstalled chrome 69 stable, the problem still existed. I can not download or upload files(dialog box not showing). Drag links, selected text and pictures on any web page will also lead to the Chrome freezes.

FYI, everything returns to normal when i downgrade back to chrome 68.

Deleted: Steps_to_reproduce_the_problem.zip 7.8 MB

Steps_to_reproduce_the_problem.zip 7.8 MB Download

As per the confirmation given by reporter in comment#5, about the file downloading dialog box pop-up, which is not seen(pop-up) from M60(60.0.3112.0) and the issue is seen in the latest chrome version(71.0.3546.0) too. Hence removing Needs-Bisect label.
Note: We are not encountering any hang/blocking of the browser i.e., the browser is responding properly without any issues.

Requesting someone from "Internals>Network" team to have a look into the issue and help in further triaging it.

Thanks!

ETW trace is attached.

Deleted: etwtraces_chrome.etl.zip 4.5 MB

etwtraces_chrome.etl.zip 4.5 MB Download

+brucedawson in case he has time to look at the attached ETW trace.

In one of the repro videos the site https://image.online-convert.com/convert-to-png is used instead and the browser hangs when the Choose File button is clicked - the one right below "Upload your image you want to convert to PNG:"

When I test this with canary and stable I cannot reproduce the hang. The file dialog shows up.

ETW traces for hangs don't tend to work very well because some of the vital information is only collected when the hang ends - and in this case it never does. A crash dump is more useful in this case. I don't have a Windows 7 machine but I believe that you can use Task Manager's Details tab to record a crash dump - right click on the right Chrome process (use Chrome's task manager to find the PID of the browser process first).

It is possible that this is a Windows 7 only bug. Has this been tested on Windows 7 lately? It could also be a localization bug of some sort but that seems less likely. It could also be related to what shell extensions are installed, 

 crbug.com/759848  is a different instance of a hang related to file dialogs - apparently COM can lead to hangs if not used extremely carefully.

I looked at Explorer.exe to see what shell extensions are installed and there are quite a few. I am quite suspicious of cfafabdaagad.dll, but any one of the other shell extensions could be causing problems in the file dialog in Chrome.

Line #, Company Name, Image Name, Image Path, File Version
2, , cfafabdaagad.dll, C:\ProgramData\cfafabdaagad.dll, 2.0.0.0
3, , nvShell.dll, C:\Program Files\NVIDIA Corporation\nview\nvShell.dll, 
4, 2ch & THEMEX, MacType64.dll, C:\Program Files\MacType\MacType64.dll, 1.2016.904.0
5, Alexander Roshal, RarExt.dll, C:\Program Files\WinRAR\RarExt.dll, 5.30.0
6, easyhook.codeplex.com, EasyHK64.dll, C:\Program Files\MacType\EasyHK64.dll, 2.7.0.0
7, Igor Pavlov, 7-zip.dll, C:\Program Files\7-Zip\7-zip.dll, 15.12
8, Microsoft Corporation, , , 
9, NVIDIA Corporation, nvshext.dll, C:\Windows\System32\nvshext.dll, 327.02
10, Tencent, QQShellExt64.dll, C:\Program Files (x86)\Tencent\TIM\ShellExt\QQShellExt64.dll, 1.2.0.21645
11, Tonec Inc., , , 
12, , IDMShellExt64.dll, C:\Program Files (x86)\Internet Download Manager\IDMShellExt64.dll, 6.28.14.20
13, , IDMNetMon64.dll, C:\Program Files (x86)\Internet Download Manager\IDMNetMon64.dll, 6.28.14.142
14, , idmbrbtn64.dll, C:\Program Files (x86)\Internet Download Manager\idmbrbtn64.dll, 6.28.14.52

If the original poster of the bug could share a crash dump that could be helpful. Removing any unexpected or unwanted shell extensions would also be wise. We should make sure that we have tested on Windows 7.

Thank you for your prompt and detailed reply. The culprit is 'cfafabdaagad.dll'. After deleting it, the problem is gone. Thanks again

Thanks for the update. Closing.

This would probably have been avoided through third-party blocking, so adding that tag. This type of bug will then be reintroduced if we move the file-picker out of process ( crbug.com/884802 ) but we will try to leave a switch so that third-party blocking can be reinstated for the file picker, to allow easier investigation of this sort of problem.

That is, once third-party blocking is enabled and  crbug.com/884802  disables it for the file picker, the first triage step for file-picker bugs will be to re-enable third-party blocking for the file picker to see if that resolves the issue.

Closing as WontFix (ExternalDependency leaves it tagged as open)