Update doc comments to follow style guide.

sdk/lib/_internal/pub/bin/pub.dart

 // Copyright (c) 2013, 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.
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:args/args.dart';
 import 'package:http/http.dart' as http;
 import 'package:path/path.dart' as path;
@@ skipping 181 matching lines @@
         'Command "${options.name}" does not take any arguments.');
   }
 
   return syncFuture(() {
     return command.run(cacheDir, options);
   }).whenComplete(() {
     command.cache.deleteTempDir();
   });
 }
 
-/// Checks that pub is running on a supported platform. If it isn't, it prints
-/// an error message and exits. Completes when the validation is done.
+/// Checks that pub is running on a supported platform.
+///
+/// If it isn't, it prints an error message and exits. Completes when the
+/// validation is done.
 Future validatePlatform() {
   return syncFuture(() {
     if (Platform.operatingSystem != 'windows') return null;
 
     return runProcess('ver', []).then((result) {
       if (result.stdout.join('\n').contains('XP')) {
         log.error('Sorry, but pub is not supported on Windows XP.');
         return flushThenExit(exit_codes.USAGE);
       }
     });
   });
 }