Added JS event listener for tab web-state.

[Brandon-T]

Security Review

• https://github.com/brave/security/issues/810

Summary of Changes

• Fix tab screenshots in TabTray
• Solidify Session Restore of dynamic pages

This pull request fixes #5180

Submitter Checklist:

• Unit Tests are updated to cover new or changed functionality
• User-facing strings use NSLocalizableString()

Reviewer Checklist:

• Issues include necessary QA labels:
  • QA/(Yes|No)
  • bug / enhancement
• Necessary security reviews have taken place.
• Adequate unit test coverage exists to prevent regressions.
• Adequate test plan exists for QA to validate (if applicable).
• Issue and pull request is assigned to a milestone (should happen at merge time).

[pes10k]

looks good to me privacy-wise, though i made a few small suggestions for cleanup and consistency

[iccub]

Good job, i ran this code for a bit and seems to work for all cases and websites

[diracdeltas]

@Brandon-T i was not done reviewing this yet - in the future please wait til sec review is closed

[Brandon-T]

@Brandon-T i was not done reviewing this yet - in the future please wait til sec review is closed

Ahh sorry. I saw the sgtm (and I read it as seems good to merge). Sorry again. I should have checked.
I can revert it and then reopen this PR.

[diracdeltas]

I can revert it and then reopen this PR.

@Brandon-T thanks, no need in this case since my comments are mostly questions. but for future reference sgtm = sounds good to me and the sec review ticket should be the source of truth.