Fix exception in checked mode

pkg/analysis_server/lib/src/services/search/search_engine.dart

 // Copyright (c) 2014, 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 services.search_engine;
 
 import 'dart:async';
 
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/visitor.dart';
@@ skipping 162 matching lines @@
     return _element;
   }
 
   /**
    * The absolute path of the file containing the match.
    */
   String get file => unitSource.fullName;
 
   @override
   int get hashCode {
-    return JenkinsSmiHash.hash4(libraryUri, unitUri, kind, sourceRange);
+    return JenkinsSmiHash.hash4(libraryUri.hashCode, unitUri.hashCode,
+        kind.hashCode, sourceRange.hashCode);
   }
 
   /**
    * Return the [LibraryElement] for the [libraryUri] in the [context].
    */
   LibraryElement get libraryElement {
     _libraryElement ??= context.getLibraryElement(librarySource);
     return _libraryElement;
   }
 
@@ skipping 72 matching lines @@
     if (element is ElementImpl) {
       if (element.codeOffset != null &&
           element.codeOffset <= offset &&
           offset <= element.codeOffset + element.codeLength) {
         containingElement = element;
         super.visitElement(element);
       }
     }
   }
 }