By popular demand, print the configurations being tested by test.dart at startup.

tools/test.dart

Index: tools/test.dart
diff --git a/tools/test.dart b/tools/test.dart
index ccc276f315602dd54557203ad921a532dcbcff5a..40ca8b37372cc70bdd8e7966cd775602eb51b4a7 100755
--- a/tools/test.dart
+++ b/tools/test.dart
@@ -54,6 +54,15 @@ main() {
   List<Map> configurations = optionsParser.parse(new Options().arguments);
   if (configurations == null) return;
 
+  // Print the configurations being run by this excution of test.dart.
+  StringBuffer sb = new StringBuffer('Test configuration');
+  sb.add(configurations.length > 1 ? 's:' : ':');
+  for (Map conf in configurations) {
+    sb.add(' ${conf["component"]}_${conf["mode"]}_${conf["arch"]}');
+    if (conf['checked']) sb.add('_checked');
+  }
+  print(sb);
+
   // Extract global options from first configuration.
   var firstConf = configurations[0];
   Map<String, RegExp> selectors = firstConf['selectors'];