Announcements and migration guides

If we do make a breaking change (defined as a change that caused one
or more of these submitted tests to require changes), we will announce
the change on our flutter-announce
mailing list as well as in our release notes.

We provide a list of guides for migrating code affected by
breaking changes.

Deprecation policy

We will, on occasion, deprecate certain APIs rather than outright
break them overnight. This is independent of our compatibility policy
which is exclusively based on whether submitted tests fail, as
described above.

Deprecated APIs are removed after a migration grace period. This grace
period is one calendar year after being released on the stable channel,
or after 4 stable releases, whichever is longer.

When a deprecation does reach end of life, we follow the same procedures
listed above for making breaking changes in removing the deprecated API.

Dart and other libraries used by Flutter