fix(privacy): Shred intermittently not clearing all data

[StephenHeaps]

Resolves brave/brave-browser#41897

Submitter Checklist:

• I confirm that no security/privacy review is needed and no other type of reviews are needed, or that I have requested them
• 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 wiki
  • npm run presubmit wiki, 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/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

1. Enable Shred feature flags in brave://flags
2. Open 'Settings' -> 'Shields & Privacy' -> 'Manage Website Data' and remove all data
3. Visit https://amazon.com / tap on favourites button (if defaults are still set).
   • Alternatively can try with a simple test site that stores data every 1ms (once you tap start button): https://stephenheaps.github.io/shred/test-local-storage.html
4. Shred the https://amazon.com tab
5. Open 'Settings' -> 'Shields & Privacy' -> 'Manage Website Data'
6. Verify no amazon.com data is displayed
7. Repeat a few times, the issue was intermittent so should test at least a few times.

[brave-builds]

Released in v1.73.54

[Uni-verse]

Verified on iPhone 12 running iOS 18.0 using version 1.73 (60)

Flags:

• #brave-shred
• #brave-shred-cache-data

---

Using test steps in brave/brave-browser#41897 (comment):

• Ensured that all data is cleared for websites when using Shred
• Ensured that data is removed with Shred via tab icon menu and tab view shred button.

example	example	example