Move mojo and mojom from mojo/public/dart to mojo/dart/packages

mojo/dart/packages/mojom/lib/src/commands/single.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 library mojom.command.single;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:args/args.dart';
@@ skipping 34 matching lines @@
   _validateArguments() async {
     await validateArguments();
 
     _package = new Directory(makeAbsolute(argResults['package']));
     log.info("package = $_package");
     if (!(await _package.exists())) {
       throw new CommandLineError("The package $_package must exist");
     }
   }
 }