Thanks for filing the issue!

Checked the issue on reported chrome version 65.0.3325.181 using Windows 10 with the below mentioned steps.
1. Launched Chrome
2. Navigated to https://gist.github.com/gudmundurarnar/8a8805b4a5060f6492937c574167f88a
3. Downloaded the zip file and extracted it.
4. Navigated to chrome://extensions -> Turned on Developer mode.
5. Tried Loading the extension. 
It shows an error while loading extension as it could not load manifest. Attaching the screen shot of the same.

@arnar: Could you please let us know if we have missed anything in the process. Any further inputs from your end may help us to triage the issue in a better way.

Tentatively adding component "Platform>Extensions", please change if this isn't apt.

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@Vamshi. 
Thanks for looking into this.

Could you check the folder structure of the extracted zip files? Is the manifest file on the top level of the directory structure? Check if there is sub-folder with the manifest file below that. 

The folder that you select when loading the extension needs to contain the manifest file at top level. (the GUID folder names are confusing)

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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

This commit (Chrome 66) seems to fix it: https://chromium.googlesource.com/chromium/src/+/d01ce6e06ab8

Unable to reproduce the issue on reported chrome version 65.0.3325.181 using Windows 10 with the below mentioned steps.
1. Launched Chrome
2. Added the extension by following Comment#3, Closed the browser.
3. Given "git clone https://gist.github.com/gudmundurarnar/8a8805b4a5060f6492937c574167f88a scrolling" in command prompt.
4. Then "cd scrolling"
5. Launched chrome with flag "--disable-features=GuestViewCrossProcessFrames"
6. Clicked on the scroll bar and scrolled down/up and moved the cursor outside of the web page.
Even after moving the cursor out of the web page we are able to see the scrolling properly with out any issues. Attaching the screen cast of the same.

@arnar: Could you please have a look at the screen cast and let us know if we have missed anything. Any further inputs from your end may help us.

CC'ing W. James MacLean from comment#5 by reporter and requesting to help in further triaging it.

Thanks!

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A step was missing from the reproduction steps.

1. Run chrome with: --disable-features=GuestViewCrossProcessFrames
2. Install the scrolling extension from: https://gist.github.com/gudmundurarnar/8a8805b4a5060f6492937c574167f88a
3. Launch the scrolling extension. A popup is opened with the site: sau.no loaded in webview.
4. In the popup from step 3, click the scrollbar and drag it up/down while holding down left mouse button. Move the cursor outside the webview region and continue mouse dragging up/down with left mouse button down.

What is the expected behavior?
The scrolling should continue even though the mouse cursor is moved slightly outside the webview region

What went wrong?
As soon as the cursor is outside the webview region the scrolling stops.

I have attached a screen recording.

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	ExtensionScrolling.mp4 779 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

Since the issue only reproduces if you use --disable-features=GuestViewCrossProcessFrames, which is not supported going forward, and since it also seems to be fixed after the commit mentioned in C#5, I'm going to mark this WontFix.

I've cc'd a group of relevant people who can let me know if there's anything we should be doing instead.