Make isEmpty a getter.

lib/core/map.dart

 // Copyright (c) 2011, 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.
 
 /**
  * A [Map] is an associative container, mapping a key to a value.
  * Null values are supported, but null keys are not.
  */
 interface Map<K, V> default HashMapImplementation<K, V> {
   /**
@@ skipping 66 matching lines @@
   Collection<V> getValues();
 
   /**
    * The number of {key, value} pairs in the map.
    */
   int get length;
 
   /**
    * Returns true if there is no {key, value} pair in the map.
    */
-  bool isEmpty();
+  bool get isEmpty;
 }
 
 /**
  * Hash map version of the [Map] interface. A [HashMap] does not
  * provide any guarantees on the order of keys and values in [getKeys]
  * and [getValues].
  */
 interface HashMap<K, V> extends Map<K, V>
     default HashMapImplementation<K, V> {
   /**
@@ skipping 16 matching lines @@
   /**
    * Creates a map with the default implementation.
    */
   LinkedHashMap();
 
   /**
    * Creates a [LinkedHashMap] that contains all key value pairs of [other].
    */
   LinkedHashMap.from(Map<K, V> other);
 }