private void resetStopwatch() {
            if (stopwatch != null) {
                stopwatch.reset().start();
            }
        }
State changes from IDLE -> PING_SCHEDULED -> PENDING_PING_ACK -> IDLE and so on. When the
channel is inactive then the state changes to SHUTDOWN.
core/src/main/java/com/linecorp/armeria/internal/common/AbstractKeepAliveHandler.java