Listen for context add/remove and unit invalidation to update the index.

pkg/analysis_server/test/services/search/search_engine2_test.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 test.services.src.search.search_engine2;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/services/index2/index2.dart';
 import 'package:analysis_server/src/services/search/search_engine.dart';
@@ skipping 52 matching lines @@
 }
 
 @reflectiveTest
 class SearchEngineImpl2Test extends AbstractSingleUnitTest {
   Index2 index;
   SearchEngineImpl2 searchEngine;
 
   void setUp() {
     super.setUp();
     index = createMemoryIndex2();
-    searchEngine = new SearchEngineImpl2(context, index);
+    searchEngine = new SearchEngineImpl2(index);
   }
 
   test_searchAllSubtypes() async {
     _indexTestUnit('''
 class T {}
 class A extends T {}
 class B extends A {}
 class C implements B {}
 ''');
     ClassElement element = findElement('T');
@@ skipping 621 matching lines @@
       Element element, List<ExpectedMatch> expectedMatches) async {
     List<SearchMatch> matches = await searchEngine.searchReferences(element);
     _assertMatches(matches, expectedMatches);
   }
 
   static void _assertMatches(
       List<SearchMatch> matches, List<ExpectedMatch> expectedMatches) {
     expect(matches, unorderedEquals(expectedMatches));
   }
 }