Implement 'help' command for Observatory debugger.

runtime/observatory/lib/src/cli/command.dart

 // Copyright (c) 2015, 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.
 
 part of cli;
 
 // Splits a line into a list of string args.
 List<String> _splitLine(String line) {
   var args = line.split(' ').where((arg) {
       return arg != ' ' && arg != '';
@@ skipping 146 matching lines @@
       // TODO(turnidge): Add a proper exception class for this.
       return new Future.error('notfound');
     } else if (commands.length == 1) {
       return commands[0].run(args.sublist(commands[0]._depth));
     } else {
       // TODO(turnidge): Add a proper exception class for this.
       return new Future.error('ambiguous');
     }
   }
 
+  // Find all matching commands.  Useful for implementing help systems.
+  List<Command> matchCommand(List<String> args, bool preferExact) {
+    if (args.isEmpty) {
+      // Adding an empty string to the end causes us to match all
+      // subcommands of the last command.
+      args.add('');
+    }
+    return _match(args, preferExact);
+  }
+
   Future run(List<String> args) {
     throw 'should-not-execute-the-root-command';
   }
 
   toString() => 'RootCommand';
 }
 
 // A node in the command tree.
 abstract class Command extends _CommandBase {
   Command(this.name, List<Command> children) : super(children);
 
-  final name;
+  final String name;
+  String get fullName {
+    if (_parent is RootCommand) {
+      return name;
+    } else {
+      return '${_parent.fullName} $name';
+    }
+  }
 
   toString() => 'Command(${name})';
 }