There are two issues in the test as written:
* There is a race on the first check to dtor_task_queue_id which might be
encountered if the calling thread is de-scheduled and the unref queue manages
to collect the object before the end of the scope.
* Two threads were owning a shared object but we relied on the object to be
collected on the unref queue.
Flow is a simple compositor based on Skia that the Flutter engine uses to cache
recoded paint commands and pixels generated from those recordings. Flow runs on
the GPU thread and uploads information to the GPU.