Use the NavigationCollector from analyzer_plugin to avoid duplication

pkg/analysis_server/lib/src/domains/analysis/navigation_dart.dart

 // Copyright (c) 2015, 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.
 
-import 'package:analysis_server/plugin/analysis/navigation/navigation_core.dart';
 import 'package:analysis_server/src/protocol_server.dart' as protocol;
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/ast/utilities.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/generated/source.dart';
+import 'package:analyzer_plugin/utilities/navigation/navigation.dart';
 
 NavigationCollector computeDartNavigation(NavigationCollector collector,
     CompilationUnit unit, int offset, int length) {
   _DartNavigationCollector dartCollector =
       new _DartNavigationCollector(collector);
   _DartNavigationComputerVisitor visitor =
       new _DartNavigationComputerVisitor(dartCollector);
   if (offset == null || length == null) {
     unit.accept(visitor);
   } else {
@@ skipping 326 matching lines @@
    */
   void _addUriDirectiveRegion(UriBasedDirective node, Element element) {
     if (element != null) {
       Source source = element.source;
       if (element.context.exists(source)) {
         computer._addRegionForNode(node.uri, element);
       }
     }
   }
 }