Adjust messaging (or remove) for side loading of extensions

Test plan

1. Open https://developer.chrome.com/extensions/samples in a new tab
2. Download one of the sample extensions and unzip
3. Visit chrome://extensions/
4. Enable developer mode
5. Click Load unpacked and then pick the folder where the extension was unzippped (step 2)
6. Warning should not be shown (see picture below for example)
7. Restart browser
8. Warning should not be shown on startup (see picture below for example)

Description

We inherit the following UI from Chromium:

We should adjust the messaging for this since we sometimes recommend certain extensions be manually installed when the Chrome store doesn’t allow them.

Note that we don’t have our own store right now, so this isn’t about policy of what should or shouldn’t be allowed.

We definitely don’t need to keep showing it every time you launch the browser.

[Mr-Mondragon]

A suggestion from #1432 is to remove notification from dev channel but keep warning in release/beta.

To be honest, this is not a good idea. This more or less ‘forces’ people to use a dev version (or put up with the nagging popups forever). I am a normal user of Brave, and as such I should be using the official version. Besides the fact that I keep things up to date with package managers, and using dev channel would cause extra maintenance effort.

[Mr-Mondragon]

Let me please stress this again, as I think security is the most important concern of all this:

Keeping the same popup showing up every time makes security WORSE, not better!

I totally understand the reasons for this popup. Really. But I have a self made developer extension, and Brave warns me every single time. Despite the fact that I am with absolute 100% certainty NOT at any risk. Extremely annoying. After doing this a 100 times or so, clicking it away becomes something automatic, you do it unconsciously.

Can you please reconsider this feature, but with two critical changes:

1. Only offer the option to not show the warning again for that specific version of that particular extension. Whenever a different extension is loaded, or if this one is changed (!) the warning should appear again.
2. Maybe make the “do not warn me again about this specific version of this particular extension” feature optional. So by default it’s not there, but you can enable a setting to get it. To protect the user from doing this accidentally.

I think overall security would be served best by this approach. Better than how it’s done now, which introduces the risk that people develop the habit of clicking away the warning automatically. Very dangerous, this is not what we want if we have security in mind.

Thank you for your consideration.