Bugfix: dark mode broken for settings when strict fingerprinting

[ShivanKaul]

Resolves brave/brave-browser#16496. Needed to add an explicit check to make sure shields are up.

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:

• Added automated test for the breakage
• Check against https://dev-pages.brave.software/fingerprinting/strict-mode.html as detailed in original PR
• Should also check for dark mode detection on Settings pages

[kjozwiak]

Adding missing 1.28.x - Nightly milestone label as this landed in master which is currently on 1.28.x.

[mj162]

@ShivanKaul, I have the reverse problem in Brave AppImage v1.31.58 in which there is no brave://settings/appearance setting for theme; the app runs in dark mode -- loved by some but disliked by others -- and cannot be changed.

[ShivanKaul]

@mj162 - do you mean brave://settings/appearance does not resolve for you? Or do you mean there is no option to change "Brave colors" on that page? I'm unable to repro either on Brave Beta v1.31.67.
If your issue persists, please create a new issue on https://github.com/brave/brave-browser/issues

[mj162]

Thanks @ShivanKaul. Original issue can be seen here:

SOLVED

Adding the following commandline options forced (a little incompletely) light mode:
--disable-features=WebUIDarkMode --enable-features=WebUILightMode

Reading related threads in summary the issues appear to be:

1. Respecting system theme (e.g. light during daytime);
2. Decoupling colour settings from privacy settings
3. Completeness of the theme setting -- e.g. right now I have daytime light mode forced on by the above command line options yet the window decoration, tabs and dropdown menus remain dark

Thanks I won't raise an issue as a) I have an imperfect workaround and b) you are awaiting an upstream fix.