code: public static <T> Observable<T> from(final ListenableFuture<T> future, final Scheduler scheduler) {
          final Worker worker = scheduler.createWorker();
          return from(future, new Executor() {
              @Override
              public void execute(final Runnable command) {
                  worker.schedule(new Action0() {
                      @Override
                      public void call() {
                          try {
                              command.run();
                          } finally {
                              worker.unsubscribe();
                          }
                      }
                  });
              }
          });
      }
docs: Converts from {@link ListenableFuture} to {@link rx.Observable}.
  
  @param future  the {@link ListenableFuture} to register a listener on.
  @param scheduler  the {@link Scheduler} where the callback will be executed.  The will be where the {@link Observer#onNext(Object)} call from.
  @return an {@link Observable} that emits the one value when the future completes.