Presubmit checks

Chromium has a system of presubmit checks which contains a lot of Chromium-specific validators we can use. The system is greatly explained here: https://www.chromium.org/developers/how-tos/depottools/presubmit-scripts/

Presubmit checks in Brave

To run presubmits in Brave: npm run presubmit, the result will be printed to the console.

There're few options you may find useful:

--base <base branch>  set the destination branch for the PR
--all                 run presubmit on all files
--files <file list>   semicolon-separated list of files to run presubmit on
--verbose [arg]       pass --verbose 2 for more debugging info

If you need to configure some upstream checks, i.e. disable or add a file filter, please use: chromium_presubmit_config.json5.

Currently upstream checks are modified in such way:

1. Make it compatible with our directory structure.
2. Disable Gerrit-specific checks.
3. Disable OWNERS/AUTHORS checks.
4. Add ability to fully disable a check or filter some files.
5. Force some checks to trigger errors instead of warnings.

Under the hood we run git cl presubmit in src/brave directory, which runs all checks from src/brave/**/PRESUBMIT.py and upstream checks from src/PRESUBMIT.py.

src/PRESUBMIT.py is modified using chromium_presubmit_overrides.py to support chromium_presubmit_config.json5.