@Nullable
  public synchronized List<ProducerContextCallbacks> setPriorityNoCallbacks(Priority priority) {
    if (priority == mPriority) {
      return null;
    }
    this.mPriority = priority;
    return new ArrayList<>(mCallbacks);
  }
Changes priority.

<p>This method does not call any callbacks. Instead, caller of this method is responsible for
iterating over returned list and calling appropriate method on each callback object. {@see
#callOnPriorityChanged}

@return list of callbacks if the value actually changes, null otherwise
imagepipeline/src/main/java/com/facebook/imagepipeline/producers/BaseProducerContext.java