Remove deprecated Strings class.

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, and utils removed.
 
@@ skipping 49 matching lines @@
   // 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') {
     List output_words = configurations.length > 1 ?
         ['Test configurations:'] : ['Test configuration:'];
     for (Map conf in configurations) {
       List settings = ['compiler', 'runtime', 'mode', 'arch']
           .mappedBy((name) => conf[name]).toList();
       if (conf['checked']) settings.add('checked');
-      output_words.add(Strings.join(settings, '_'));
+      output_words.add(settings.join('_'));
     }
-    print(Strings.join(output_words, ' '));
+    print(output_words.join(' '));
   }
 
   var testSuites = new List<TestSuite>();
   for (var conf in configurations) {
     if (selectors.containsKey('co19')) {
       testSuites.add(new Co19TestSuite(conf));
     }
     if (conf['runtime'] == 'vm' && selectors.containsKey('vm')) {
       // vm tests contain both cc tests (added here) and dart tests (added in
       // [TEST_SUITE_DIRECTORIES]).
@@ skipping 26 matching lines @@
       maxProcesses,
       maxBrowserProcesses,
       progressIndicator,
       startTime,
       printTiming,
       testSuites,
       () => TestingServerRunner.terminateHttpServers(),
       verbose,
       listTests);
 }