Remove uses of the old plugin model from the analysis server

pkg/analysis_server/lib/src/domains/analysis/occurrences.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/occurrences/occurrences_core.dart';
-import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/protocol_server.dart' as protocol;
-import 'package:analyzer/exception/exception.dart';
-import 'package:analyzer/src/generated/engine.dart'
-    show AnalysisContext, AnalysisEngine;
-import 'package:analyzer/src/generated/source.dart' show Source;
-
-/**
- * Compute all known occurrences for the given [source].
- */
-OccurrencesCollectorImpl computeOccurrences(
-    AnalysisServer server, AnalysisContext context, Source source) {
-  OccurrencesCollectorImpl collector = new OccurrencesCollectorImpl();
-  List<OccurrencesContributor> contributors =
-      server.serverPlugin.occurrencesContributors;
-  for (OccurrencesContributor contributor in contributors) {
-    try {
-      contributor.computeOccurrences(collector, context, source);
-    } catch (exception, stackTrace) {
-      AnalysisEngine.instance.logger.logError(
-          'Exception from occurrences contributor: ${contributor.runtimeType}',
-          new CaughtException(exception, stackTrace));
-    }
-  }
-  return collector;
-}
 
 /**
  * A concrete implementation of [OccurrencesCollector].
  */
 class OccurrencesCollectorImpl implements OccurrencesCollector {
   Map<protocol.Element, protocol.Occurrences> elementOccurrences =
       <protocol.Element, protocol.Occurrences>{};
 
   List<protocol.Occurrences> get allOccurrences {
     return elementOccurrences.values.toList();
   }
 
   @override
   void addOccurrences(protocol.Occurrences current) {
     protocol.Element element = current.element;
     protocol.Occurrences existing = elementOccurrences[element];
     if (existing != null) {
       List<int> offsets = _merge(existing.offsets, current.offsets);
       current = new protocol.Occurrences(element, offsets, existing.length);
     }
     elementOccurrences[element] = current;
   }
 
   static List<int> _merge(List<int> a, List<int> b) {
     return <int>[]..addAll(a)..addAll(b);
   }
 }