Make copy of the drivers list in SearchEngineImpl2 to avoid ConcurrentModificationError.

pkg/analysis_server/lib/src/services/search/search_engine_internal2.dart

 // Copyright (c) 2016, 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 'dart:async';
 
 import 'package:analysis_server/src/services/search/search_engine.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart';
 import 'package:analyzer/src/dart/analysis/search.dart';
@@ skipping 21 matching lines @@
       }
     }
 
     await addSubtypes(type);
     return allSubtypes;
   }
 
   @override
   Future<List<SearchMatch>> searchMemberDeclarations(String name) async {
     List<SearchMatch> allDeclarations = [];
-    for (AnalysisDriver driver in _drivers) {
+    List<AnalysisDriver> drivers = _drivers.toList();
+    for (AnalysisDriver driver in drivers) {
       List<Element> elements = await driver.search.classMembers(name);
       allDeclarations.addAll(elements.map(_SearchMatch.forElement));
     }
     return allDeclarations;
   }
 
   @override
   Future<List<SearchMatch>> searchMemberReferences(String name) async {
     List<SearchResult> allResults = [];
-    for (AnalysisDriver driver in _drivers) {
+    List<AnalysisDriver> drivers = _drivers.toList();
+    for (AnalysisDriver driver in drivers) {
       List<SearchResult> results =
           await driver.search.unresolvedMemberReferences(name);
       allResults.addAll(results);
     }
     return allResults.map(_SearchMatch.forSearchResult).toList();
   }
 
   @override
   Future<List<SearchMatch>> searchReferences(Element element) async {
     List<SearchResult> allResults = [];
-    for (AnalysisDriver driver in _drivers) {
+    List<AnalysisDriver> drivers = _drivers.toList();
+    for (AnalysisDriver driver in drivers) {
       List<SearchResult> results = await driver.search.references(element);
       allResults.addAll(results);
     }
     return allResults.map(_SearchMatch.forSearchResult).toList();
   }
 
   @override
   Future<List<SearchMatch>> searchSubtypes(ClassElement type) async {
     List<SearchResult> results = await _searchDirectSubtypes(type);
     return results.map(_SearchMatch.forSearchResult).toList();
   }
 
   @override
   Future<List<SearchMatch>> searchTopLevelDeclarations(String pattern) async {
     List<SearchMatch> allDeclarations = [];
     RegExp regExp = new RegExp(pattern);
-    for (AnalysisDriver driver in _drivers) {
+    List<AnalysisDriver> drivers = _drivers.toList();
+    for (AnalysisDriver driver in drivers) {
       List<Element> elements = await driver.search.topLevelElements(regExp);
       allDeclarations.addAll(elements.map(_SearchMatch.forElement));
     }
     return allDeclarations;
   }
 
   Future<List<SearchResult>> _searchDirectSubtypes(ClassElement type) async {
     List<SearchResult> allResults = [];
-    for (AnalysisDriver driver in _drivers) {
+    List<AnalysisDriver> drivers = _drivers.toList();
+    for (AnalysisDriver driver in drivers) {
       List<SearchResult> results = await driver.search.subTypes(type);
       allResults.addAll(results);
     }
     return allResults;
   }
 }
 
 class _SearchMatch implements SearchMatch {
   @override
   final String file;
@@ skipping 88 matching lines @@
     }
     if (kind == SearchResultKind.WRITE) {
       return MatchKind.WRITE;
     }
     if (kind == SearchResultKind.INVOCATION) {
       return MatchKind.INVOCATION;
     }
     return MatchKind.REFERENCE;
   }
 }