Move cookie list override logic to account for uninitialized preferences

[antonok-edm]

The previous implementation only iterated through lists that existed in the preferences already, so in practice it would only override lists that had enabled: false - i.e. lists that had been enabled and disabled again before the "touched" preference was introduced.

This fix clones the preferences dictionary and adds the cookie list with enabled: true to the cloned dictionary if the override should occur.

Resolves brave/brave-browser#20308

Submitter Checklist:

• I confirm that no security/privacy review is needed, or that I have requested one
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• 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)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• 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:

Same as #11621

[emerick]

LGTM, just had one minor comment - up to you if you make that change, though.

[antonok-edm]

Android CI failure is unrelated, merging.

[stephendonner]

Verified PASSED using

Brave	1.36.14 Chromium: 97.0.4692.71 (Official Build) nightly (64-bit)
Revision	adefa7837d02a07a604c1e6eff0b3a09422ab88d-refs/branch-heads/4692@{#1247}
OS	Windows 10 Version 20H2 (Build 19042.1415)

Followed the testplan from #11621.

Steps:

1. Visit https://digikey.com and confirm that a cookie notice is shown. It will appear either as a banner at the top, or as a popup along the bottom depending on window size.
2. Visit brave://flags and enable the #brave-adblock-cookie-list-default flag, then restart the browser.
3. Visit https://digikey.com and confirm that no cookie notice is shown.
4. Visit brave://adblock and confirm that the entry for Easylist-Cookie List - Filter Obtrusive Cookie Notices under Additional filters exists and is checked.
5. Return to brave://flags and set #brave-adblock-cookie-list-default to Disabled, and restart the browser.
6. Visit https://digikey.com and confirm that the cookie notice is shown again.
7. Visit brave://adblock and confirm that the entry for Easylist-Cookie List - Filter Obtrusive Cookie Notices is no longer checked.
8. Manually toggle the Easylist-Cookie List - Filter Obtrusive Cookie Notices entry to be enabled, then repeat steps 2-5.
9. Visit brave://adblock and confirm that the entry for Easylist-Cookie List - Filter Obtrusive Cookie Notices is checked.
10. Manually toggle the Easylist-Cookie List - Filter Obtrusive Cookie Notices entry to be disabled.
11. Visit brave://flags and enable the #brave-adblock-cookie-list-default flag, then restart the browser.
12. Visit brave://adblock and confirm that the entry for Easylist-Cookie List - Filter Obtrusive Cookie Notices is unchecked.
13. Visit https://digikey.com and confirm that the cookie notice is shown.

step1	step 2	step 3	step 4	step 5	step 6	step 7

step 8a	step 8b	step 8c	step 9	step 10	step 11	step 12	step 13