Remove DDG search toggle from private tabs

[emerick]

Resolves brave/brave-browser#18486

Submitter Checklist:

• I confirm that no security/privacy review is needed, or that I have requested one
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• 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, npm run lint, 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/Custom-Headers
  • 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:

• Clean profile
• Set brave.use_alternate_private_search_engine preference to false
• Launch browser
• Open Private Tab
• Verify that Private Tab shows new design and no DDG toggle
• Clean profile
• Set brave.use_alternate_private_search_engine preference to true
• Launch browser
• Open Private Tab
• Verify that Private Tab shows new design and DDG toggle
• Verify that toggle works as expected

[petemill]

Error in Storybook:

[2021-10-07T22:06:16.648Z] ERR! => Failed to build the preview
[2021-10-07T22:06:16.648Z] ERR! /home/ubuntu/workspace/pr-brave-browser-remove-ddg-search-toggle-from-private-tabs-linux/src/brave/components/brave_new_tab_ui/stories/privateNTP/privateWindow.tsx
[2021-10-07T22:06:16.648Z] ERR! [tsl] ERROR in /home/ubuntu/workspace/pr-brave-browser-remove-ddg-search-toggle-from-private-tabs-linux/src/brave/components/brave_new_tab_ui/stories/privateNTP/privateWindow.tsx(64,16)
[2021-10-07T22:06:16.648Z] ERR!       TS2551: Property 'showAlternativePrivateSearchEngine' does not exist on type 'PrivateTab'. Did you mean 'useAlternativePrivateSearchEngine'?

[simonhong]

We will show new toggle button again even if user turned off by using new toggle button?

[emerick]

The idea here is that we'll only show the alternative search provider toggle button to the user if they've already enabled it in the past; if they never enabled the alternative search engine (which would be most users), we will no longer show the toggle that enables it on this page.

cc: @rebron to double-check my understanding of how this should work...

[simonhong]

This will be called whenever new tab is created.
Instead, how about setting this in ctor of PrivateWindowSearchEngineProviderService?
PrivateWindowSearchEngineProviderService is only instantiated for private profile with non-qwant region.

[emerick]

Great point, @simonhong - fixed.

[emerick]

@petemill Fixed the storybook, sorry about that!

[Tonev]

@emerick

Does your pull request take into consideration the following issue with DuckDuckGo in private windows?

brave/brave-browser#17556

Asking because you're putting work into the DuckDuckGo search functionality in private windows, but if the aforementioned issue remains unsolved, users who would like to keep using DuckDuckGo will still have to use Show autocomplete in address bar.

[simonhong]

++ for c++ with one nit.
I'll past js fils review to @petemill

[simonhong]

nit: As we don't use false for value, I think we can remove value from parameter list.

[emerick]

Good point, fixed.

[petemill]

Nit: it would be good to add a toggle to storybook so that it can see the search variation now that it's hidden by a state Boolean. Can definitely be a follow up.