@SuppressWarnings("MissingOverride") // For compilation with Java < 9.
    public BiFunction<SSLSocket, List<String>, String> getHandshakeApplicationProtocolSelector() {
        return selector;
    }
A version of ConscryptEngineSocket that includes the new Java 9 (and potentially later
patches of 8) {@code setHandshakeApplicationProtocolSelector} API (which requires Java 8 for
compilation, due to the use of {@link BiFunction}).
common/src/main/java/org/conscrypt/Java8EngineSocket.java