Make --no-include-sdk the default for docgen

pkg/docgen/bin/docgen.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:io';
 
 import 'package:args/args.dart';
 import 'package:logging/logging.dart';
 import 'package:path/path.dart' as path;
 
@@ skipping 90 matching lines @@
       });
   parser.addFlag('verbose', abbr: 'v',
       help: 'Output more logging information.', negatable: false,
       callback: (verbose) {
         if (verbose) Logger.root.level = Level.FINEST;
       });
   parser.addFlag('include-private',
       help: 'Flag to include private declarations.', negatable: false);
   parser.addFlag('include-sdk',
       help: 'Flag to parse SDK Library files.',
-      defaultsTo: true,
+      defaultsTo: false,
       negatable: true);
   parser.addFlag('parse-sdk',
       help: 'Parses the SDK libraries only.',
       defaultsTo: false, negatable: false);
   parser.addOption('package-root',
       help: 'Sets the package root of the library being analyzed.');
   parser.addFlag('compile', help: 'Clone the documentation viewer repo locally '
       '(if not already present) and compile with dart2js', defaultsTo: false,
       negatable: false);
   parser.addFlag('serve', help: 'Clone the documentation viewer repo locally '
@@ skipping 24 matching lines @@
         'To start at some other page, e.g. for a package, provide the name '
         'of the package in this argument, e.g. --start-page=intl will make '
         'the start page of the viewer be the intl package.',
         defaultsTo: null);
   parser.addFlag('indent-json',
       help: 'Indents each level of JSON output by two spaces',
       defaultsTo: false, negatable: true);
 
   return parser;
 }