Only print stdout/stderr if we've got an unexpected output

tools/testing/dart/test_runner.dart

Index: tools/testing/dart/test_runner.dart
diff --git a/tools/testing/dart/test_runner.dart b/tools/testing/dart/test_runner.dart
index 1f20e6e02dc6f0d30efef72ac51f11f17725e84f..95a0532d08d5cf861cb23519317a3c28f8fc4498 100644
--- a/tools/testing/dart/test_runner.dart
+++ b/tools/testing/dart/test_runner.dart
@@ -1692,7 +1692,7 @@ class ProcessQueue {
     // Otherwise we need to enqueue it again into the test queue.
     if (lastCommandCompleted || timedOut || nonZeroExitCode) {
       var verbose = testCase.configuration['verbose'];
-      if (nonZeroExitCode && verbose != null && verbose) {
+      if (lastCommandOutput.unexpectedOutput && verbose != null && verbose) {
         print(testCase.displayName);
         print("stderr:");
         print(decodeUtf8(lastCommandOutput.stderr));