Fix for 'Concurrent modification during iteration' during search.

pkg/analyzer/lib/src/dart/analysis/file_state.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:convert';
 import 'dart:typed_data';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/error/listener.dart';
@@ skipping 557 matching lines @@
       this._resourceProvider,
       this._sourceFactory,
       this._analysisOptions,
       this._salt) {
     _testView = new FileSystemStateTestView(this);
   }
 
   /**
    * Return the known files.
    */
-  Iterable<FileState> get knownFiles =>
-      _pathToFiles.values.map((files) => files.first);
+  List<FileState> get knownFiles =>
+      _pathToFiles.values.map((files) => files.first).toList();
 
   @visibleForTesting
   FileSystemStateTestView get test => _testView;
 
   /**
    * Return the canonical [FileState] for the given absolute [path]. The
    * returned file has the last known state since if was last refreshed.
    *
    * Here "canonical" means that if the [path] is in a package `lib` then the
    * returned file will have the `package:` style URI.
@@ skipping 115 matching lines @@
         .where((f) => f._transitiveFiles == null)
         .toSet();
   }
 
   Set<FileState> get filesWithoutTransitiveSignature {
     return state._uriToFile.values
         .where((f) => f._transitiveSignature == null)
         .toSet();
   }
 }