…and avoid `SurfaceProducer` returning invalid `Surface` (flutter#169899)> [!NOTE]> For anyone reviewing this PR, seeflutter/packages#9360 for how I'd use the`getSurface(boolean forceNewSurface)` method.> [!NOTE]> For anyone coming across this PR post-landing, in the code reviewprocess, I renamed `getSurface(boolean forceNewSurface)` to`getForcedNewSurface()`.(1) Adds method `getSurface(boolean forceNewSurface)` to`SurfaceProducer` that will force the creation of a new `Surface` when`SurfaceProducer.getSurface()` is called.(2) Fixes `SurfaceProducer` to avoid returning invalid `Surface`s when`SurfaceProducer.getSurface()`/`getSurface(boolean forceNewSurface)` iscalled.My motivation for adding this is directly tied toflutter#155294. The`camera_android_camerax` plugin supports a camera preview use case thatrequires providing a `Surface` to in order to render the preview. Itdoes so via `SurfaceProducer`; we provide a `Surface` retrieved from`SurfaceProducer.getSurface()` to the CameraX library to render a camerapreview, and when the camera preview is done, a callback that we provideis called, reporting that `Surface` as used and that it now should bereleased/invalidated (see[`SurfaceRequest`](https://developer.android.com/reference/androidx/camera/core/SurfaceRequest),[`SurfaceRequest.Result`](https://developer.android.com/reference/androidx/camera/core/SurfaceRequest#provideSurface(android.view.Surface,java.util.concurrent.Executor,androidx.core.util.Consumer%3Candroidx.camera.core.SurfaceRequest.Result%3E))).However, the CameraX library [makes noguarantees](https://developer.android.com/reference/androidx/camera/core/Preview.SurfaceProvider#onSurfaceRequested(androidx.camera.core.SurfaceRequest):~:text=The%20camera%20may%20repeatedly%20request%20surfaces%20throughout%20usage%20of%20a%20Preview%20use%20case%2C%20but%20only%20a%20single%20request%20will%20be%20active%20at%20a%20time.)about when requests for new `Surface`s are made, so the following racecondition can happen:1. CameraX requests a `Surface`2. We provide `Surface` A from `SurfaceProducer.getSurface()`3. The camera preview was paused; CameraX requests a new `Surface`4. The camera preview is resumed5. We provide `Surface` A from `SurfaceProducer.getSurface()` because itis still technically valid6. CameraX calls our callback and now `Surface` A is released/invalidI believe `SurfaceProducer` currently has no way to handle the level ofcomplexity of `Surface` handling required for use cases like the`camera_android_camerax` camera preview, where a `Surface` may beinvalidated between calls to `SurfaceProducer.getSurface()`. So,`getSurface(boolean forceNewSurface)` can support these use cases.*`getSurface(boolean forceNewSurface)` simply will force`SurfaceProducer` to return a new `Surface` when`SurfaceProducer.getSurface` is called versus potentially returning thesame `Surface` as the previous invocation.For `camera_android_camerax`, seeflutter/packages#9360 for an example of how itwould be used.*I'd like to note that I also played around with creating new`SurfaceProducer`s to solve the camera problem, which _was_ successfuland probably could be generally for that use case, but I think it'scleaner to support this functionality from within the same`SurfaceProducer` since we can 🤷‍♀️ It also helps avoid the user fromneeding to create/manage multiple Flutter `Texture`s, from myunderstanding.forceNewSurface)` to never return an invalid `Surface`sI noticed that `SurfaceProducer.getSurface()`/`getSurface(booleanforceNewSurface)` does not check for `Surface` validity before returningthem while I was working on (1). Honestly, this just feels right? Weshould ensure that a `Surface` is valid and can be used before returningit and potentially confusing the user.- [x] I read the [Contributor Guide] and followed the process outlinedthere for submitting PRs.- [x] I read the [Tree Hygiene] wiki page, which explains myresponsibilities.- [x] I read and followed the [Flutter Style Guide], including [Featureswe expect every widget to implement].- [x] I signed the [CLA].- [x] I listed at least one issue that this PR fixes in the descriptionabove.- [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 DrivenFixes] where supported.- [x] All existing and new tests are passing.If you need help, consider asking for advice on the #hackers-new channelon [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