android/guava/src/com/google/common/util/concurrent/AbstractFuture.java
final void maybePropagateCancellationTo(@NullableDecl Future<?> related) {
    if (related != null & isCancelled()) {
      related.cancel(wasInterrupted());
    }
  }
final void maybePropagateCancellationTo(@NullableDecl Future<?> related) {
    if (related != null & isCancelled()) {
      related.cancel(wasInterrupted());
    }
  }
If this future has been cancelled (and possibly interrupted), cancels (and possibly interrupts)
the given future (if available).