WIP: First rev attempt at removing the deprecated cosmetic filter

[bsclifton]

Fixes brave/brave-browser#8914

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
  • Android
  • iOS
  • Linux
  • macOS
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• Verified that these changes pass automated tests (unit, browser, security tests) on
  • iOS
  • Linux
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• 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
  • https://github.com/brave/brave-browser/wiki/QA-Guide

Test Plan:

1. Right click a page (any page)
2. There should no longer be a Brave context menu item

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.

[bsclifton]

All JavaScript unit tests pass - built locally and verified nothing is being thrown via stdout. Could you check this out a little more in-depth, @antonok-edm 😄

[antonok-edm]

Just one small modification and this should be good to go.

I'd also raise one more possibility before fully getting rid of this - if users have added any of the old cosmetic filters, I think it should be possible to pull them out of storage, turn them into custom filters on brave://adblock, and clear the storage entirely. In practice though, I'm sure a good number of the rules overlap with ones in the default cosmetic adblock lists, and anyone who used that feature is probably technical enough to update them manually on a site-by-site basis anyways - it might not be worth the extra machinery.

[antonok-edm]

By the way, most of the testing for the newer system is actually in C++ browser tests. I'd recommend npm run test -- brave_browser_tests --filter='Cosmetic*.*' to verify this hasn't broken anything.

[bsclifton]

@antonok-edm thanks for the above feedback 😄 Just addressed those items

As for preserving the existing rules, I'm not sure if this was a well-known enough feature to warrant that kind of migration. I'll check with a few folks and circle back

[pes10k]

just for my two cents, I second @bsclifton 's idea. Unless its very simple to migrate them, i think its probably not worth the trouble :)

[bsclifton]

OK going to go ahead and close this up, after discussion 😄