CompletableFuture<ResponseHeaders> headersFuture() {
            return headersFuture;
        }
Creates a new {@link DefaultSplitHttpResponse} from the specified {@link HttpResponse}.
The specified {@link Predicate} is used to determine if the {@link ResponseHeaders} is the final one.
For example, if there are multiple informational {@link ResponseHeaders} and the {@link Predicate}
will be {@code headers -> !headers.status().isInformational()}.
However, if the {@link ResponseHeaders} is only one, and it can be an informational one such as a
WebSocket response, {@link Predicate} will be {@code headers -> true}.
core/src/main/java/com/linecorp/armeria/internal/common/DefaultSplitHttpResponse.java