This document explains the Chromium policies for files in the
User Data directory.
Due to the nature of frequent updates, Chromium must always support loading data from files written by previous versions. A good rule of thumb is to leave migration code in place for at least one year (approximately 9 milestones with the current 6-week release cadence). It is not uncommon for clients to update from very old versions, so use good judgement for deciding when to remove migration code -- if the complexity is low, keep it indefinitely.
In cases where Chromium is run against a
User Data directory written by a newer version, the browser may run to the extent possible with the following behaviors:
Breaking changes in data storage are forbidden once a branch has been created for a release. This guarantees that data written by a later build on a release branch can be read by previous versions on that same release branch.