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

pkg/analysis_server/lib/src/server/driver.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 driver;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:math';
 
@@ skipping 325 matching lines @@
     CommandLineParser parser = _createArgParser();
     ArgResults results = parser.parse(arguments, <String, String>{});
     if (results[HELP_OPTION]) {
       _printUsage(parser.parser);
       return;
     }
 
     // TODO (danrubel) Remove this workaround
     // once the underlying VM and dart:io issue has been fixed.
     if (results[INTERNAL_DELAY_FREQUENCY] != null) {
-      AnalysisServer.performOperationDelayFreqency =
+      AnalysisServer.performOperationDelayFrequency =
           int.parse(results[INTERNAL_DELAY_FREQUENCY], onError: (_) => 0);
     }
 
     int port;
     bool serve_http = false;
     if (results[PORT_OPTION] != null) {
       serve_http = true;
       try {
         port = int.parse(results[PORT_OPTION]);
       } on FormatException {
@@ skipping 241 matching lines @@
    */
   static void _rollLogFiles(String path, int numOld) {
     for (int i = numOld - 1; i >= 0; i--) {
       try {
         String oldPath = i == 0 ? path : '$path.$i';
         new File(oldPath).renameSync('$path.${i+1}');
       } catch (e) {}
     }
   }
 }