Change output of test.dart --list option, so it can be parsed automatically.

tools/testing/dart/test_progress.dart

Index: tools/testing/dart/test_progress.dart
diff --git a/tools/testing/dart/test_progress.dart b/tools/testing/dart/test_progress.dart
index d3e14005482fdf068fb2b5a91ac79d359f5b5297..334dec0a35800dd6d27fa23b7570f9bbba0e5e0e 100644
--- a/tools/testing/dart/test_progress.dart
+++ b/tools/testing/dart/test_progress.dart
@@ -24,6 +24,8 @@ class ProgressIndicator {
         return new LineProgressIndicator(startTime, printTiming);
       case 'verbose':
         return new VerboseProgressIndicator(startTime, printTiming);
+      case 'silent':
+        return new SilentProgressIndicator(startTime, printTiming);
       case 'status':
         return new StatusProgressIndicator(startTime, printTiming);
       case 'buildbot':
@@ -183,6 +185,18 @@ class ProgressIndicator {
 }
 
 
+class SilentProgressIndicator extends ProgressIndicator {
+  SilentProgressIndicator(Date startTime, bool printTiming)
+      : super(startTime, printTiming);
+  void testAdded() { }
+  void start(TestCase test) { }
+  void done(TestCase test) { }
+  void allTestsKnown() { }
+  void allDone() {
+    exit(0);
+  }
+}
+
 class CompactIndicator extends ProgressIndicator {
   CompactIndicator(Date startTime, bool printTiming)
       : super(startTime, printTiming);