Do not show percentages when we don't know what they are in test progress indication.

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 2f9a3212d64acb6c7b85d9d879394c03473a6b10..297e46c1bd79d41f7d587b3cde33a971423fd7a9 100644
--- a/tools/testing/dart/test_runner.dart
+++ b/tools/testing/dart/test_runner.dart
@@ -326,12 +326,12 @@ class ProcessQueue {
   void _checkDone() {
     // When there are no more active test listers ask for more work
     // from process queue users.
-    if (_activeTestListers == 0 &&
-        !_enqueueMoreWork(this) &&
-        _tests.isEmpty() &&
-        _numProcesses == 0) {
-      _terminateDartcBatchRunners();
-      _progress.allDone();
+    if (_activeTestListers == 0 && !_enqueueMoreWork(this)) {
+      _progress.allTestsKnown();
+      if (_tests.isEmpty() && _numProcesses == 0) {
+        _terminateDartcBatchRunners();
+        _progress.allDone();
+      }
     }
   }