Block tab.loadURL in tor tabs until tor is initialized

[diracdeltas]

Fix #14680

Test Plan:

1. open brave, turn on showing bookmarks toolbar and showing home button
   in about:preferences. bookmark some sites.
2. open tor tab and try to click on bookmarks before tor finishes
   loading. also try clicking on the home button and clicking the
   History > Home menu item.
3. these loads should be blocked until tor finishes initializing

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).
• 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. (Ask a Brave employee to help if you cannot access this document.)

Test Plan:

Reviewer Checklist:

• Request a security/privacy review as needed if one was not already requested.

Tests

• Adequate test coverage exists to prevent regressions
• Tests should be independent and work correctly when run individually or as a suite ref
• New files have MPL2 license header

[bsclifton]

Worked perfectly! Nice and clean implementation too. Great job 😄👍

[bsclifton]

master 1cf53e1
0.24.x 8d65141
0.23.x e11f16a