Reset stopwatch when we had results on AdsStream rather than change the delay calculation logic.

Author: larry-safran

xds/src/main/java/io/grpc/xds/client/ControlPlaneClient.java

@@ -446,14 +446,18 @@ private void handleRpcStreamClosed(Status status) {
         // Reset the backoff sequence if had received a response, or backoff sequence
         // has never been initialized.
         retryBackoffPolicy = backoffPolicyProvider.get();
+        stopwatch.reset();
       }
 
       // FakeClock in tests isn't thread-safe. Schedule the retry timer before notifying callbacks
       // to avoid TSAN races, since tests may wait until callbacks are called but then would run
       // concurrently with the stopwatch and schedule.
+
+      long elapsed = stopwatch.elapsed(TimeUnit.NANOSECONDS);
+      long delayNanos = Math.max(0, retryBackoffPolicy.nextBackoffNanos() - elapsed);
+
       rpcRetryTimer =
-          syncContext.schedule(new RpcRetryTask(), retryBackoffPolicy.nextBackoffNanos(),
-              TimeUnit.NANOSECONDS, timeService);
+          syncContext.schedule(new RpcRetryTask(), delayNanos, TimeUnit.NANOSECONDS, timeService);
 
       Status newStatus = status;
       if (responseReceived) {