
`availableFrameCount` tracks the number of frames that is avilable on the `SurfaceTexture`, but haven't been used (by `updateTexImage()`) yet. Thus semantically this counter should only be decremented after calling `updateTexImage()`, not before it. Also reworded `getPendingFrameCount()` javadoc, "external texture" is an internal state that is not publicised anywhere. PiperOrigin-RevId: 488765174