Add --step_name option to test.dart.

dart/tools/testing/dart/test_progress.dart

Index: dart/tools/testing/dart/test_progress.dart
diff --git a/dart/tools/testing/dart/test_progress.dart b/dart/tools/testing/dart/test_progress.dart
index 8066899209c7e1e3cad83f0a429642c4b0ca209c..7b99f678cd4627d3d0e3bfd3d539f532feb5d629 100644
--- a/dart/tools/testing/dart/test_progress.dart
+++ b/dart/tools/testing/dart/test_progress.dart
@@ -340,6 +340,8 @@ class StatusProgressIndicator extends ProgressIndicator {
 
 
 class BuildbotProgressIndicator extends ProgressIndicator {
+  static String stepName;
+
   BuildbotProgressIndicator(Date startTime, bool printTiming)
       : super(startTime, printTiming);
 
@@ -359,15 +361,8 @@ class BuildbotProgressIndicator extends ProgressIndicator {
 
   void _printFailureSummary() {
     if (!_failureSummary.isEmpty()) {
-      // We need to create a unique name for each step, otherwise, the
-      // build bot will show the same failure when several steps
-      // fail. We don't know the name of the current step as it is
-      // printed by the program invoking this.
-      // TODO(ahe): Pass in the step name as an option, and let
-      // test.py take care of printing the steps.
-      var name = 'failures ($_startTime)';
       print('@@@STEP_FAILURE@@@');
-      print('@@@BUILD_STEP $name@@@');
+      print('@@@BUILD_STEP $stepName failures@@@');
     }
     super._printFailureSummary();
   }