@Nullable
  @Override
  public <T> T getExtra(String key) {
    //noinspection unchecked
    return (T) mExtras.get(key);
  }
Calls {@code onPriorityChanged} on each element of the list. Does nothing if list == null
imagepipeline/src/main/java/com/facebook/imagepipeline/producers/BaseProducerContext.java