Cleans up pre-populated search engines.

[mkarolin]

Engines kept:

• Google
• Duckduckgo
• Qwant
• Bing
• Startpage.

Adds a unit test to verify the search engines overridden by us are used
instead of the original ones.

Lint fixes.

Fixes brave/brave-browser#3316

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
  • Windows
  • macOS
  • Linux
• Verified that these changes pass automated tests (npm test brave_unit_tests && npm test brave_browser_tests) on
  • Windows
  • macOS
  • Linux
• 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

Test Plan:

Automated testing:
npm run test -- brave_unit_tests --filter=BraveTemplateURLPrepopulateDataTest.*
npm run test -- brave_unit_tests --filter=BraveTemplateURLServiceUtilTest.*

Manual testing:

1. Test transition from pre-existing profile; default not changed.

• Start Brave version prior to version that contains this change,
• Navigate to brave://settings/searchEngines and verify that the default search engine has not been
  changed (e.g. Google for U.S., Qwant for DE & FR),
• Exit Brave,
• Start Brave version that contains this change,
• Navigate to brave://settings/searchEngines and verify that only the 5 engines listed above are
  present and that the default engine has not changed.

2. Test transition from pre-existing profile; default changed.

• Start Brave version prior to version that contains this change,
• Navigate to brave://settings/searchEngines and change the default search engine to Amazon,
• Exit Brave,
• Start Brave version that contains this change,
• Navigate to brave://settings/searchEngines and verify that only the 5 engines listed above + Amazon
  are present and that the default engine is Amazon.

3. Test new profile.

• Start Brave version that contains this change with a fresh profile,
• Navigate to brave://settings/searchEngines and verify that only the 5 engines listed above are present
  and that Qwant is the default engine for DE & FR and Google for all others.

4. Test import from Muon; removed engine.

• Start Brave (Muon) and change the default search engine to Amazon, exit the browser,
• Start Brave version that contains this change with a fresh profile,
• In the Welcome screen, click next, then Import,
• Pick import from Brave (old) and leave all boxes checked,
• Finish import,
• Navigate to brave://settings/searchEngines and verify that Google (or Qwant for DE, FR locales)
  remains the default engine.

5. Test import from Muon; kept engine.

• Start Brave (Muon) and change the default search engine to DuckDuckGo, exit the browser,
• Start Brave version that contains this change with a fresh profile,
• In the Welcome screen, click next, then Import,
• Pick import from Brave (old) and leave all boxes checked,
• Finish import,
• Navigate to brave://settings/searchEngines and verify that DuckDuckGo is set as the
  default engine.

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

[simonhong]

Tested this PR on MacOS and works great. Also all manual tests works as expected.

[diracdeltas]

@mkarolin we are also discussing keeping yahoo; let me cc you on the discussion in slack

[diracdeltas]

👍 confirmed these are the 5 we want to keep

[bbondy]

Thanks @mkarolin, could you do uplift PRs too?

[bsclifton]

Did a rebase (sorry for invaliding review! in case you wanted to re-approve, @simonhong)

[simonhong]

++

[bsclifton]

For future PRs, it might be better to have two commits; one fixing the issue and the second fixing linting errors... but awesome work 😄👍

[bsclifton]

Trying to uplift; looks like this works cleanly on dev (0.61.x) #1674

But appears to be some conflicts when uplifting to beta... @mkarolin can you check this out?

[mojoaxel]

🎉