43599a528afb681eff407c5fb1d0d9ef981c5064
nextId when using createSurfaceProducer with SurfaceTextures (flutter/engine#50011)
The change is _very_ tiny, but I added some documentation as well. After this PR, it appears we're "ready" to start using this API once it lands in stable. Hoorah! Here are local tests using `video_player_android/example`: ## Skia  ## Impeller 
Do not double-increment
nextId when using createSurfaceProducer with SurfaceTextures (flutter/engine#50011)
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