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This functionality is useful in a custom DrivenScrollActivity subclass, just like it's useful in a BallisticScrollActivity subclass. For example, if one calls `animateTo(0, …)` to scroll to the beginning of a list, there will be no overscroll (provided the chosen curve doesn't go beyond its endpoint). The same is true if one calls `animateTo(position.maxScrollExtent, …)` to scroll to the end... as long as the value of maxScrollExtent at the beginning remains accurate when the scroll view reaches the end. If one wants to scroll to the end and avoid overscroll even when that turns out to be closer than the initial estimate found in maxScrollExtent, then that calls for customizing the overscroll behavior of a DrivenScrollActivity. Fortunately we don't need to invent any new API in order to do this: BallisticScrollActivity already has an API for the exact same need. So copy that API -- name, docs, and all -- to keep these two classes aligned. (It might also be useful to take much of what these have in common and factor that out to a common subclass; but that'd be for another PR.) ## Pre-launch Checklist - [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [x] I read the [Tree Hygiene] wiki page, which explains my responsibilities. - [x] I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement]. - [x] I signed the [CLA]. - [ ] I listed at least one issue that this PR fixes in the description above. - [x] I updated/added relevant documentation (doc comments with `///`). - [x] I added new tests to check the change I am making, or this PR is [test-exempt]. - [x] I followed the [breaking change policy] and added [Data Driven Fixes] where supported. - [x] All existing and new tests are passing. If you need help, consider asking for advice on the #hackers-new channel on [Discord]. <!-- Links --> [Contributor Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview [Tree Hygiene]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md [test-exempt]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests [Flutter Style Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md [Features we expect every widget to implement]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement [CLA]: https://cla.developers.google.com/ [flutter/tests]: https://github.com/flutter/tests [breaking change policy]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes [Discord]: https://github.com/flutter/flutter/blob/main/docs/contributing/Chat.md [Data Driven Fixes]: https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md
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