guava-gwt/src-super/com/google/common/util/concurrent/super/com/google/common/util/concurrent/GwtFluentFutureCatchingSpecialization.java
public final FluentFuture<V> catching(
      Class<Throwable> exceptionType,
      Function<? super Throwable, ? extends V> fallback,
      Executor executor) {
    return (FluentFuture<V>) Futures.catching(this, exceptionType, fallback, executor);
  }
public final FluentFuture<V> catching(
      Class<Throwable> exceptionType,
      Function<? super Throwable, ? extends V> fallback,
      Executor executor) {
    return (FluentFuture<V>) Futures.catching(this, exceptionType, fallback, executor);
  }
/*
In the GWT versions of the methods (below), every exceptionType parameter is required to be
Class<Throwable>. To handle only certain kinds of exceptions under GWT, you'll need to write
your own instanceof tests.