Prevent system theme change affect brave's theme in linux

[simonhong]

fix brave/brave-browser#30766

Recently, upstream introduced DarkModeManagerLinux that monitor platform's color scheme change.
If that change noti arrives after initializing brave theme with brave's theme option,
brave's activated theme could be different with brave's option.

When we have sysem default theme option in linux also, we could enable.

Resolves

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
• 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 lint, 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/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:

Please refer to the issue for various experiences from many linux users.

STR 1.

1. Set os theme as light
2. Set dark mode to brave theme and relaunch
3. Check dark mode is still applied

NOTE: It seems it's not 100% reproducible. Maybe it depends on distributions/window manager and etc...

STR 2.

1. Launch brave
2. Change os theme and check brave's theme is not changed

[kjozwiak]

Verification PASSED on PopOS 22.04 x64 using the following build(s):

Brave | 1.54.82 Chromium: 115.0.5790.40 (Official Build) beta (64-bit)
--- | ---
Revision | 071c9ddea889c3c7887daf4eac13fed72d4fff62-refs/branch-heads/5790@{#979}
OS | Linux

Verified that theming is working as expected on Linux using the STR/Cases outlined via #18922 (comment) as per the following:

Ensured that Brave is always using the correct theming when switching the OS theme. Examples of cases:

• ensured that Brave uses Dark theme when set even though the OS theme is set as Light
• ensured that Brave uses Light theme when set even though the OS theme is set as Dark
• ensured that restarting multiple times didn't cause Brave to use the incorrect theme.

Example	Example

Also ensured that Use GTK was working correctly. When Use GTK, ensured that OS elements match the current theme but the theme shouldn't be changed within Brave. Confirmed with @simonhong on this point.

Example	Example

Example	Example

[MartinNowak]

fix brave/brave-browser#30766

Recently, upstream introduced DarkModeManagerLinux that monitor platform's color scheme change. If that change noti arrives after initializing brave theme with brave's theme option, brave's activated theme could be different with brave's option.

@simonhong @goodov
This unfortunately no longer allows to follow the system theme :/, something people have waited the better part of 3 years for.
998903 - XDG Desktop Portal "Prefer dark appearance" does not affect prefers-color-scheme media query - chromium

It's good to fix the inconsistency with Brave's setting, but maybe it should be a a tri-state switch instead (use-system, dark, light)?

There also seems to be system dark-mode support on MacOS and Windows.

brave-core/browser/themes/brave_dark_mode_utils_linux.cc

Line 15 in e441fe5

// Linux doesn't support system dark theme so there is no chance to set

[NANASHI0X74]

I find it quite disappointing that brave opted to disable this feature rather than making it properly accessible in the settings.
Or is this something that chromium would have to implement upstream?

[NANASHI0X74]

I guess this is the relevant feature request: brave/brave-browser#14685
it's been said there that the "waiting upstream" label should be removed.
Could you confirm this/update the labels?

[simonhong]

@rebron I think we need to consider about adding Same as linux entry to Brave colors optoion like we do on macOS/Windows.

[NANASHI0X74]

@rebron I think we need to consider about adding Same as linux entry to Brave colors optoion like we do on macOS/Windows.

I've got half a mind to submit a PR for this myself after waiting for years for this feature and given that chromium has finally implemented it, but I've a hard time navigating the codebase. Could you perhaps outline in broad strokes what needs to be done, which files need editing would also be helpful.

[light-on-shadow]

Any chance we see this regression fixed? It's an absolute deal breaker, completely stopped using the browser for now.

[SlowNicoFish]

@rebron I think we need to consider about adding Same as linux entry to Brave colors optoion like we do on macOS/Windows.

I've got half a mind to submit a PR for this myself after waiting for years for this feature and given that chromium has finally implemented it, but I've a hard time navigating the codebase. Could you perhaps outline in broad strokes what needs to be done, which files need editing would also be helpful.

I would also like to do this. Trying to get in running on my machine