ellyjones@ / avi@
This document introduces the concept of flag ownership in Chromium.
See also Chromium Flag Expiry.
Look through //chrome/browser/flag-metadata.json for flags that your team added, maintains, or cares about. For each such flag you find, either:
If it is still in use: ensure that the entries in the owners list are correct (see the comment at the top of the file) and that an appropriate expiration milestone is set;
If it is not in use: delete the entry from the //chrome/browser/flag-metadata.json file, and delete it from kFeatureEntries in //chrome/browser/about_flags.cc or //ios/chrome/browser/flags/about_flags.mm for iOS. Remember to file a cleanup bug to remove code paths that become dead.
When the flag ownership project started, many of the hundreds of flags in chrome://flags were obsolete and unused, but each of them represented configuration surface that was exposed to users and to QA. Worse, obsolete flags often prevented removal of legacy code paths that were not used in the field but were still reachable via a flag setting.
The flag ownership project has dealt with that by moving Chromium towards a model where chrome://flags entries are what they were originally intended to be: temporary, experimental options. Each flag must have a set owner who can keep track of whether or when that flag should expire and an express time by which it will expire, either because the feature it controls will have become default-enabled or because the feature it controls will have been cancelled.
Note that this change only affects chrome://flags entries, not features controlled via FeatureList (commonly used to run Finch trials) or command-line switches.
Some flags do not control UI features, but rather are commonly-used debugging controls, such as ignore-gpu-blocklist. For these flags, see the instructions at the head of flag-metadata.json. Please be very judicious about never-expiring flags, since they represent ongoing engineering, test and support burden. The flags team will probably only approve your non-expiring flag if:
If you have a non-expiring flag, the flags team requires a comment in the json file as to the rationale that it be non-expiring. A quick sentence or two will be fine. (Yes, we are aware that, technically, JSON files can‘t have comments. Don’t worry about it.) You'll also need to add your flag to the permitted list in //chrome/browser/flag-never-expire-list.json which will require approval from the flags team.
A good rule of thumb is that your flag should expire one milestone after you expect your feature to have launched to stable. In other words, if your feature will be 100% enabled on Stable in M74, your flag should be marked as expiring in M75.
Please do not stress about the expiration date. The purpose of the expiration milestone is to let us remove abandoned flags. Pick a reasonable milestone by which you'll be done with the flag; you can always adjust it later if your schedule changes.
Please get in touch with flags-dev@chromium.org. If you feel like you need to have a Google-internal discussion for some reason, there's also chrome-flags@.