Remove deprecated Strings class.

tools/ddbg.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.
 
 // Simple interactive debugger shell that connects to the Dart VM's debugger
 // connection port.
 
 import "dart:io";
 import "dart:json" as json;
 import "dart:utf";
@@ skipping 538 matching lines @@
   };
 }
 
 void main() {
   Options options = new Options();
   List<String> arguments = options.arguments;
   if (arguments.length > 0) {
     arguments = <String>['--debug', '--verbose_debug']..addAll(arguments);
     Process.start(options.executable, arguments).then((Process process) {
       process.onExit = (int exitCode) {
-        print('${Strings.join(arguments, " ")} exited with $exitCode');
+        print('${arguments.join(" ")} exited with $exitCode');
       };
       process.stdin.close();
       // Redirecting both stdout and stderr of the child process to
       // stdout.  This should help users keep track of which errors
       // are coming from the debugger, and which errors are coming
       // from the process being debugged.
       process.stderr.pipe(stdout);
       process.stdout.pipe(stdout);
       debuggerMain();
     });
   } else {
     debuggerMain();
   }
 }