A DESCRIPTION OF THE PROBLEM :
Make java.lang.Process implement AutoCloseable in order to make it possible to use in a try-with-resources block. It is too easy in exceptional cases to not properly close a Process. This could leave a Process running even outside of the life of the JVM. Additionally, there may be some InputStreams that are not closed promptly.

The close() method could implement a graceful shutdown similar to the below pseudo code (possibly allowing the grace period to be defined in java.lang.ProcessBuilder):
  if (supportsNormalTermination()) {
    destroy();
    if (waitFor(5, TimeUnit.SECONDS)) {
      return;
    }
  }
  destroyForcibly().waitFor();

There is precedence for adding AutoCloseable to existing abstract classes and interfaces like java.net.http.HttpClient (JDK-8304165) and java.util.concurrent.ExecutorService (JDK-8285450).