We created an annotation processor in #842695, but it isn't currently turned on as there are various places in the existing code where the assertion fails. 

The processor ensures that a method with a @UiThread annotation in running on the UI thread, and that a method with a @WorkerThread annotation is running on a background thread.
 

We created an annotation processor in 842695, but it isn't currently turned on as there are various places in the existing code where the assertion fails. 

The processor ensures that a method with a @UiThread annotation in running on the UI thread, and that a method with a @WorkerThread annotation is running on a background thread.