Remove string concatenation with + from all Dart files in tools directory.

tools/test-runtime.dart

 #!/usr/bin/env dart
 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // TODO(ager): Get rid of this version of test.dart when we don't have
 // to worry about the special runtime checkout anymore.
 // This file is identical to test.dart with test suites in the
 // directories samples, client, compiler, frog, and utils removed.
 
@@ skipping 35 matching lines @@
   var maxProcesses = firstConf['tasks'];
   var progressIndicator = firstConf['progress'];
   var verbose = firstConf['verbose'];
   var printTiming = firstConf['time'];
   var listTests = firstConf['list'];
 
   // Print the configurations being run by this execution of
   // test.dart. However, don't do it if the silent progress indicator
   // is used. This is only needed because of the junit tests.
   if (progressIndicator != 'silent') {
-    StringBuffer sb = new StringBuffer('Test configuration');
-    sb.add(configurations.length > 1 ? 's:' : ':');
+    List output_words = configurations.length > 1 ?
+        ['Test configurations:'] : ['Test configuration:'];
     for (Map conf in configurations) {
-      sb.add(' ${conf["compiler"]}_${conf["runtime"]}_${conf["mode"]}_' +
-          '${conf["arch"]}');
-      if (conf['checked']) sb.add('_checked');
+      List settings =
+          ['compiler', 'runtime', 'mode', 'arch'].map((name) => conf[name]);
+      if (conf['checked']) settings.add('checked');
+      output_words.add(Strings.join(settings, '_'));
     }
-    print(sb);
+    print(Strings.join(output_words, ' '));
   }
 
   var configurationIterator = configurations.iterator();
   bool enqueueConfiguration(ProcessQueue queue) {
     if (!configurationIterator.hasNext()) {
       return false;
     }
 
     var conf = configurationIterator.next();
     if (selectors.containsKey('co19')) {
@@ skipping 18 matching lines @@
 
   // Start process queue.
   var queue = new ProcessQueue(maxProcesses,
                                progressIndicator,
                                startTime,
                                printTiming,
                                enqueueConfiguration,
                                verbose,
                                listTests);
 }