WIP: Toss cookies and other browsing data for New Tor Identity.

[riastradh-brave]

fix brave/brave-browser#3872

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Verified that these changes build without errors on
  • Windows
  • macOS
  • Linux
• Verified that these changes pass automated tests (npm test brave_unit_tests && npm test brave_browser_tests && npm run test-security) on
  • Windows
  • macOS
  • Linux
• Verified that all lint errors/warnings are resolved (npm run lint)
• Ran git rebase master (if needed).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Request a security/privacy review as needed.
• Add appropriate QA labels (QA/Yes or QA/No) to include the closed issue in milestone
• Public documentation has been updated as necessary. 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-Protection-Mode
  • 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-issues-with-tracking-protection

Test Plan:

1. Open a private window with Tor.
2. Log into https://trac.torproject.org/ with cypherpunks/writecode.
3. Hamburger menu ⟶ New Tor Identity
4. Confirm that you are now logged out of trac.torproject.org.

Reviewer Checklist:

• New files have MPL-2.0 license header.
• Request a security/privacy review as needed.
• Adequate test coverage exists to prevent regressions
• Verify test plan is specified in PR before merging to source

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.

[bridiver]

there are definitely problems with this approach and it also shouldn't be in browser_commands anyway, this kind of stuff should be handled by the browser context or the tor service

[bridiver]

I'm not sure any of this is necessary because I believe we're already using a new partition/network context when cycling, but this not only has race conditions, it will also cause problems for other tabs because it deletes data across the entire browser context, not just the individual tab

[bbondy]

Is this still valid? No updates for a month. Thanks.

[riastradh-brave]

This is a draft that doesn't quite work right and that isn't worth revisiting until after we have introduced a mechanism for first-party isolation, which is higher-priority. So, not abandoned, but not mergeable yet.

[bsclifton]

Closing as stale. We can keep the branch of course, in case we wanted to revisit