Be more consistent about how we mark classes that can't be extended.

[Hixie]

Fixes #26095

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test-exempt.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[flutter-dashboard]

It looks like this pull request may not have tests. Please make sure to add tests before merging. If you need an exemption to this rule, contact Hixie on the #hackers channel in Chat.

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing.

[Piinks]

Are these ones different?

• TickerFuture
• PlatformViewsService
• RawKeyboard
• TextInput
• DoNothingIntent - this one looks like a special case

[a14n]

nit: update comment of modified constructors to have the same comment everywhere.

[Hixie]

@Piinks Yeah, those are meant to be instantiated but only by code in their own file. I could have a separate comment for those if you like.

@a14n There's three different cases: interfaces, classes that just contain statics, and classes instantiated locally. They have different comments. Did you find another kind of comment?

[a14n]

There's three different cases: interfaces, classes that just contain statics, and classes instantiated locally. They have different comments. Did you find another kind of comment?

Not really. I didn't really pay attention that they were 3 different cases. So it looks good.

[fluttergithubbot]

This pull request is not suitable for automatic merging in its current state.

• The status or check suite Google testing has failed. Please fix the issues identified (or deflake) before re-applying this label.