Flip .packages server support bit.

pkg/analysis_server/lib/src/server_options.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.
 
 library analysis_server.src.server_options;
 
 import 'dart:collection';
 import 'dart:io';
 
 import 'package:path/path.dart' as path;
@@ skipping 71 matching lines @@
   /// Get a String value for this `key` or [defaultValue] if undefined
   /// or not a String.
   String getStringValue(String key, {String defaultValue: null}) {
     var value = _options[key];
     if (value is String) {
       return value;
     }
     return defaultValue;
   }
 
-  /// Test whether the given [booleanPropertyKey] is set to the value `true`.
+  /// Test whether the given [booleanPropertyKey] is set to the value `true`,
+  /// falling back to [defaultValue] if undefined.
   /// For example:
   ///     myDebugOption1:true
   ///     myDebugOption2:TRUE # Also true (case and trailing whitespace are ignored).
   ///     myDebugOption3:false
   ///     myDebugOption4:off  # Treated as `false`.
   ///     myDebugOption5:on   # Also read as `false`.
-  bool isSet(String booleanPropertyKey) => _options[booleanPropertyKey] == true;
+  bool isSet(String booleanPropertyKey, {bool defaultValue: false}) {
+    var value = _options[booleanPropertyKey];
+    if (value == null) {
+      return defaultValue;
+    }
+    return value == true;
+  }
 
   void _readOptions(String contents) {
     var doc = loadYaml(contents);
     if (doc is YamlMap) {
       doc.forEach((k, v) {
         if (k is String) {
           _options[k] = v;
         }
       });
     }
   }
 }