Background

Preferences are a generic system for storing configuration parameters in Chrome, see Preferences and chrome/browser/prefs/README.md.

Individual preferences may be declared as syncable, meaning they will be uploaded to the user's Google Account and propagate across signed-in/syncing devices from the same user.

This folder contains the code for synchronizing preferences. See components/sync/README.md for background about Sync itself.

Adding syncable preferences

Making a pref syncable requires a few things:

• Specify appropriate PrefRegistrationFlags to the Register*Pref call.
• Add an entry to the appropriate SyncablePrefsDatabase: ChromeSyncablePrefsDatabase if the pref is in chrome/, IOSChromeSyncablePrefsDatabase if it‘s in ios/chrome/, or CommonSyncablePrefsDatabase if it’s cross-platform.

Important: Adding syncable prefs may have privacy impact. It‘s the responsibility of the code reviewer to ensure that new syncable prefs don’t have undue privacy impact. In particular:

• If the pref contains URLs (example: site permissions), it must be marked as is_history_opt_in_required = true, and it will only be synced if the user has opted in to history sync.
• If the pref is marked as “priority” (syncer::PRIORITY_PREFERENCES or syncer::OS_PRIORITY_PREFERENCES), then it will not be encrypted. Carefully consider if it actually needs to be “priority”. (The most common reason for this is when the pref needs to be consumed on the server side.)
• In any other cases that are unclear or questionable, reach out to chrome-privacy-core@google.com, or to rainhard@ directly.