This document explains the Chromium policies for files in the User Data
directory.
[TOC]
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.