Implement hashCode for classes with equals().

editor/util/plugins/com.google.dart.java2dart/resources/java_engine.dart

 library java.engine;
 
 class StringUtilities {
   static const String EMPTY = '';
   static const List<String> EMPTY_ARRAY = const <String> [];
   static String intern(String s) => s;
   static String substringBefore(String str, String separator) {
     if (str == null || str.isEmpty) {
       return str;
     }
@@ skipping 19 matching lines @@
 }
 
 class ArrayUtils {
   static List addAll(List target, List source) {
     List result = new List.from(target);
     result.addAll(source);
     return result;
   }
 }
 
+class ObjectUtilities {
+  static int combineHashCodes(int first, int second) => first * 31 + second;
+}
+
 class UUID {
   static int __nextId = 0;
   final String id;
   UUID(this.id);
   String toString() => id;
   static UUID randomUUID() => new UUID((__nextId).toString());
 }