Issue 21419. Don't create navigation region for elements without location.

pkg/analysis_server/lib/src/computer/computer_navigation.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 computer.navigation;
 
 import 'package:analysis_server/src/protocol_server.dart' as protocol;
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/scanner.dart';
@@ skipping 18 matching lines @@
     return new List.from(_regions);
   }
 
   void _addRegion(int offset, int length, Element element) {
     if (element is FieldFormalParameterElement) {
       element = (element as FieldFormalParameterElement).field;
     }
     if (element == null || element == DynamicElementImpl.instance) {
       return;
     }
+    if (element.location == null) {
+      return;
+    }
     protocol.Element target = protocol.newElement_fromEngine(element);
     _regions.add(new protocol.NavigationRegion(offset, length, [target]));
   }
 
   void _addRegion_nodeStart_nodeEnd(AstNode a, AstNode b, Element element) {
     int offset = a.offset;
     int length = b.end - offset;
     _addRegion(offset, length, element);
   }
 
@@ skipping 177 matching lines @@
     Element element = node.bestElement;
     computer._addRegionForNode(node, element);
   }
 
   void _safelyVisit(AstNode node) {
     if (node != null) {
       node.accept(this);
     }
   }
 }