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

tools/test-runtime.dart

Index: tools/test-runtime.dart
diff --git a/tools/test-runtime.dart b/tools/test-runtime.dart
index c366a73d1456ea245c51453c276e828aec14ed28..4fc1257bf19e5b118db86735d0b639292888de98 100755
--- a/tools/test-runtime.dart
+++ b/tools/test-runtime.dart
@@ -27,6 +27,14 @@ 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(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'];