Fix checked mode failure in the debugger.

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:convert";
 import "dart:io";
 import "dart:async";
@@ skipping 103 matching lines @@
     [ new HelpCommand(),
       new QuitCommand(),
       new RunCommand(),
       new KillCommand(),
       new ConnectCommand(),
       new DisconnectCommand(),
       new SetCommand(),
       new ShowCommand() ];
 
 
-Command matchCommand(String commandName, bool exactMatchWins) {
+List<Command> matchCommand(String commandName, bool exactMatchWins) {
   List matches = [];
   for (var command in commandList) {
     if (command.name.startsWith(commandName)) {
       if (exactMatchWins && command.name == commandName) {
         // Exact match
         return [command];
       } else {
         matches.add(command);
       }
     }
@@ skipping 1274 matching lines @@
       handleUncaughtError: debuggerError));
 
   zone.run(() {
       parseArgs(args);
       cmdo = new Commando(completer: debuggerCommandCompleter);
       cmdSubscription = cmdo.commands.listen(processCommand,
                                              onError: processError,
                                              onDone: processDone);
     });
 }