Add extensions support for Tor OTR profile

[darkdh]

This PR

1. Leverage "Allow in private" to enable a extension in Tor
2. When a extension is running in spanning mode, warn users that network requests made by the extension will not go through Tor
   (https://developers.chrome.com/extensions/manifest/incognito)

Security review submitted: https://github.com/brave/security/issues/258
Resolves brave/brave-browser#2761

We can only merge this PR after master upgrade to 88.0.4284.0, otherwise Tor OTR profile won't be destroyed even there is no Tor window opened and that will leave zombie private extensions.
This is the change we need
https://chromium-review.googlesource.com/c/chromium/src/+/2434925/6/chrome/browser/ui/browser.cc#605
Master has already upgraded to C88

Submitter Checklist:

• There is a ticket for my issue.
• Used Github auto-closing keywords in the commit message.
• Wrote a good PR/commit description
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally: npm run test -- brave_browser_tests, npm run test -- brave_unit_tests, npm run lint, npm run gn_check, npm run tslint
• Ran git rebase master (if needed).
• Requested a security/privacy review as needed.

Reviewer Checklist:

• New files have MPL-2.0 license header.
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on.
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Custom-Headers
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

Enable extension in Tor

1. Install any extension
2. Visit brave://extensions/ and click Details of the extension
3. Turn on Allow in private
4. The extension should be accessible in Tor window

Spanning vs Split

1. Extensions run in spanning mode by default so go to the extension page of Enable extension in Tor
2. We should see warning text like this
3. Go to user profile folder, find the extension folder with the id seen in extension page
4. Copy the folder to somewhere
5. Open the copied folder and find manifest.json
6. Edit manifest.json and add "incognito": "split", and save.
7. Visit brave://extensions/ and turn on developer mode and click Load unpacked
8. Choose the copied folder
9. It should load the copied version of the extension
10. Go to the detail of the extension, we should see warning text like

[petemill]

As suggested in DM, I suggest injecting the HTML and JS for the new toggle directly to the chromium component via RegisterPolymerTemplateModifications and RegisterPolymerComponentBehaviors, so that you can keep the directly-applied styles for the row instead of having to copy/paste. You also wouldn't need this patch or the .js file patch.

[darkdh]

fixed

[bridiver]

did you check with @petemill on this? At the very least it can be compressed to one line

[darkdh]

Known CI issue

16:22:24  Failing tests:
16:22:24  	TestTargetName:
16:22:24  		-[AdsWrapperTest testPreferencePersistance]
16:22:24  
16:22:24  ** TEST EXECUTE FAILED **

https://ci.brave.com/job/pr-brave-browser-tor-extensions-support-ios/20/execution/node/216/log/