Make isEmpty a getter.

utils/pub/git_source.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.
 
 library git_source;
 
 import 'git.dart' as git;
 import 'io.dart';
 import 'package.dart';
 import 'source.dart';
@@ skipping 60 matching lines @@
     if (description is String) return;
     if (description is! Map || !description.containsKey('url')) {
       throw new FormatException("The description must be a Git URL or a map "
           "with a 'url' key.");
     }
     description = new Map.from(description);
     description.remove('url');
     description.remove('ref');
     if (fromLockFile) description.remove('resolved-ref');
 
-    if (!description.isEmpty()) {
+    if (!description.isEmpty) {
       var plural = description.length > 1;
       var keys = Strings.join(description.getKeys(), ', ');
       throw new FormatException("Invalid key${plural ? 's' : ''}: $keys.");
     }
   }
 
   /**
    * Two Git descriptions are equal if both their URLs and their refs are equal.
    */
   bool descriptionsEqual(description1, description2) {
@@ skipping 125 matching lines @@
 
   /**
    * Returns [description] if it's a description, or [PackageId.description] if
    * it's a [PackageId].
    */
   _getDescription(description) {
     if (description is PackageId) return description.description;
     return description;
   }
 }