Apply patch from https://codereview.chromium.org/10967042/.

pkg/args/lib/args.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.
 
 /**
  * This library lets you define parsers for parsing raw command-line arguments
  * into a set of options and values using [GNU][] and [POSIX][] style options.
  *
  * ## Defining options ##
  *
@@ skipping 161 matching lines @@
  * Will display something like:
  *
  *     --mode            The compiler configuration
  *                       [debug, release]
  *
  *     --[no-]verbose    Show additional diagnostic info
  *     --arch            The architecture to compile for
  *
  *           [arm]       ARM Holding 32-bit chip
  *           [ia32]      Intel x86
+ * 
+ * To assist the formatting of the usage help, single line help text will
+ * be followed by a single new line. Options with multi-line help text
+ * will be followed by two new lines. This provides spatial diversity between
+ * options.
  *
  * [posix]: http://pubs.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap12.html#tag_12_02
  * [gnu]: http://www.gnu.org/prep/standards/standards.html#Command_002dLine-Interfaces
  */
 #library('args');
 
 #import('dart:math');
 
 // TODO(rnystrom): Use "package:" URL here when test.dart can handle pub.
 #import('src/utils.dart');
@@ skipping 579 matching lines @@
       allowedBuffer.add(allowed);
       if (allowed == option.defaultValue) {
         allowedBuffer.add(' (default)');
       }
       first = false;
     }
     allowedBuffer.add(']');
     return allowedBuffer.toString();
   }
 }