Would it be possible to remove the final modifier from HttpBackOffUnsuccessfulResponseHandler#handleResponse [1] so it lets a chance to log or trigger something? (without having to rewrite it)
HttpBackOffIOExceptionHandler [2] does not have the final modifier for instance.

[1] https://github.com/googleapis/google-http-java-client/blob/master/google-http-client/src/main/java/com/google/api/client/http/HttpBackOffUnsuccessfulResponseHandler.java#L139
[2] https://github.com/googleapis/google-http-java-client/blob/master/google-http-client/src/main/java/com/google/api/client/http/HttpBackOffIOExceptionHandler.java#L108

Environment details

• OS: Linux Ubuntu
• Java version: 1.8.0_181
• google-http-java-client version: 1.27.0