feat(ntp): store last NTP search engine as a pref

[IanKrieger]

Resolves brave/brave-browser#41789

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:

Currently, the search engine that is the default for the search-widget on the New Tab Page (NTP), is managed by localStorage. For more information on what localStorage is, please see documentation on the Web Storage API. This feature intends on replacing the value which is stored as a property of the window, and instead have it be a preference of the browser. This way, there is no way that it can be unintentionally lost.

Prerequisite

If you do not see the NTP search widget, on the NTP go to the Customize button on the bottom right, and got to the Search settings, flip the switch on.

• By default, this should select brave search (it could be different based on your region)
• Close and open browser to see it remains the default

Enabling different engines

In the Search section of the settings, check / uncheck engines as seen fit.

• If only 1 engine is selected, de-selecting it will remove the NTP widget
• When re-enabling the search-widget, the last search engine you had set should be the one that is enabled when turning on

Changing NTP widget default

• click the search logo on the widget
• if no other engines are selected, you can use customize list to use more

Existing Profile Considerations

• If an engine is selected other than the default for your region, this should not change back to the default

Single Search Engine Selected

Scenario 1

• change default engine in settings, ensuring there is only one selected (i.e bing)
• see that change is reflected in widget
• close browser
• open browser
• ensure the search engine you recently set is the same (i.e bing)

Scenario 2

• change default engine in settings, ensuring there is only one selected (i.e ddg)
• see that change is reflected in widget
• If NTP search is enabled, disable it
• close browser
• open browser
• enable NTP search
• ensure the search engine you recently set is the same (i.e ddg)

Multiple Search Engine Selected

• Select multiple engines in settings
• Click the widget icon to see that multiple engines are available for use

Scenario 1

• change default engine using widget icon (i.e bing)
• see that change is reflected in widget
• close browser
• open browser
• ensure the search engine you recently set is the same (i.e bing)

Scenario 2

• change default using widget icon (i.e ddg)
• see that change is reflected in widget
• If NTP search is enabled, disable it
• close browser
• open browser
• enable NTP search
• ensure the search engine you recently set is the same (i.e ddg)
• ensure all selected engines are still selected

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[tmancey]

LGTM++ 🚀

[fallaciousreasoning]

lgtm! Thanks @IanKrieger for making those changes, looks much neater now!

[brave-builds]

Released in v1.73.51