Fix default search logic for Tor window and guest window

[bsclifton]

Fixes brave/brave-browser#6476

Specifically fixes:

• crash that was happening when expected search (regular DDG) was not found
• toggle (slider) status for DDG on guest window

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
  • Windows
• Verified that these changes pass automated tests (unit, browser, security tests) on
  • iOS
  • Linux
  • macOS
  • Windows
• 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:

I ran through the following:

Germany

Search in...

• regular window
• private window
• click toggle on private window and search
• Tor window
• guest window
• toggle for guest window DDG is checked (if DDG default)

Australia

Search in...

• regular window
• private window
• click toggle on private window and search
• Tor window
• guest window
• toggle for guest window DDG is checked (if DDG default)

New Zealand

Search in...

• regular window
• private window
• click toggle on private window and search
• Tor window
• guest window
• toggle for guest window DDG is checked (if DDG default)

Ireland

Search in...

• regular window
• private window
• click toggle on private window and search
• Tor window
• guest window
• toggle for guest window DDG is checked (if DDG default)

USA

Search in...

• regular window
• private window
• click toggle on private window and search
• Tor window
• guest window
• toggle for guest window DDG is NOT checked (DDG is not default)

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.

[simonhong]

I think we can do some cleanup TorWindow... and GuestWindow....
When I implemented them at first, each one's provider could be changed via its settings page. but we don't provide settings page of tor window or guest window.
If we don't have a plan to add it again, I think many codes could be deleted.

[bsclifton]

I think we can do some cleanup TorWindow... and GuestWindow....
When I implemented them at first, each one's provider could be changed via its settings page. but we don't provide settings page of tor window or guest window.
If we don't have a plan to add it again, I think many codes could be deleted.

That would be a good follow up for sure - not sure if that should be done in this PR (this needs to go back to 0.70, for C78)

How do things look otherwise, @simonhong? 😄

[bsclifton]

Given the manual testing done + full CI passing (and the need for a build soon), I'm going to merge this one 👍