code: @CheckReturnValue
      @BackpressureSupport(BackpressureKind.FULL)
      @SchedulerSupport(SchedulerSupport.NONE)
      public final <V> Flowable<T> timeout(Function<? super T, ? extends Publisher<V>> itemTimeoutIndicator, Flowable<? extends T> other) {
          ObjectHelper.requireNonNull(other, "other is null");
          return timeout0(null, itemTimeoutIndicator, other);
      }
docs: Returns a Flowable that mirrors the source Publisher, but that switches to a fallback Publisher if
  an item emitted by the source Publisher doesn't arrive within a window of time after the emission of the
  previous item, where that period of time is measured by a Publisher that is a function of the previous
  item.
  <p>
  <img width="640" height="400" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/timeout4.png" alt="">
  <p>
  Note: The arrival of the first source item is never timed out.
  <dl>
  <dt><b>Backpressure:</b></dt>
  <dd>The operator honors backpressure from downstream. The {@code Publisher}
  sources are expected to honor backpressure as well.
  If any of the source {@code Publisher}s violate this, it <em>may</em> throw an
  {@code IllegalStateException} when the source {@code Publisher} completes.</dd>
  <dt><b>Scheduler:</b></dt>
  <dd>This version of {@code timeout} operates by default on the {@code immediate} {@link Scheduler}.</dd>
  </dl>
  
  @param <V>
  the timeout value type (ignored)
  @param itemTimeoutIndicator
  a function that returns a Publisher, for each item emitted by the source Publisher, that
  determines the timeout window for the subsequent item
  @param other
  the fallback Publisher to switch to if the source Publisher times out
  @return a Flowable that mirrors the source Publisher, but switches to mirroring a fallback Publisher
  if an item emitted by the source Publisher takes longer to arrive than the time window defined
  by the selector for the previously emitted item
  @see <a href="http://reactivex.io/documentation/operators/timeout.html">ReactiveX operators documentation: Timeout</a>