Use precomputed uriBytes while computing cycle signature.

pkg/front_end/lib/src/incremental/file_state.dart

 // Copyright (c) 2017, 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 'dart:convert';
 import 'dart:typed_data';
 
 import 'package:convert/convert.dart';
 import 'package:crypto/crypto.dart';
 import 'package:front_end/file_system.dart';
 import 'package:front_end/src/base/resolve_relative_uri.dart';
 import 'package:front_end/src/dependency_walker.dart' as graph;
 import 'package:front_end/src/fasta/translate_uri.dart';
 import 'package:front_end/src/incremental/byte_store.dart';
 import 'package:front_end/src/incremental/format.dart';
@@ skipping 10 matching lines @@
 ///
 /// The properties are not guaranteed to represent the most recent state
 /// of the file system. To update the file to the most recent state, [refresh]
 /// should be called.
 class FileState {
   final FileSystemState _fsState;
 
   /// The absolute URI of the file.
   final Uri uri;
 
+  /// The UTF8 bytes of the [uri].
+  final List<int> uriBytes;
+
   /// The resolved URI of the file in the file system.
   final Uri fileUri;
 
   bool _exists;
   List<int> _content;
   List<int> _contentHash;
   bool _hasMixinApplication;
   List<int> _apiSignature;
 
   List<NamespaceExport> _exports;
   List<FileState> _importedLibraries;
   List<FileState> _exportedLibraries;
   List<FileState> _partFiles;
 
   Set<FileState> _directReferencedFiles = new Set<FileState>();
   List<FileState> _directReferencedLibraries = <FileState>[];
   Set<FileState> _transitiveFiles;
 
   /// This flag is set to `true` during the mark phase of garbage collection
   /// and set back to `false` for survived instances.
   bool _gcMarked = false;
 
-  FileState._(this._fsState, this.uri, this.fileUri);
+  FileState._(this._fsState, this.uri, this.fileUri)
+      : uriBytes = UTF8.encode(uri.toString());
 
   /// The MD5 signature of the file API as a byte array.
   /// It depends on all non-comment tokens outside the block bodies.
   List<int> get apiSignature => _apiSignature;
 
   /// The content of the file.
   List<int> get content => _content;
 
   /// The MD5 hash of the [content].
   List<int> get contentHash => _contentHash;
@@ skipping 32 matching lines @@
   List<LibraryCycle> get topologicalOrder {
     var libraryWalker = new _LibraryWalker();
     libraryWalker.walk(libraryWalker.getNode(this));
     return libraryWalker.topologicallySortedCycles;
   }
 
   /// Return the set of transitive files - the file itself and all of the
   /// directly or indirectly referenced files.
   Set<FileState> get transitiveFiles {
     if (_transitiveFiles == null) {
-      _transitiveFiles = new Set<FileState>();
+      _transitiveFiles = new Set<FileState>.identity();
 
       void appendReferenced(FileState file) {
         if (_transitiveFiles.add(file)) {
           file._directReferencedFiles.forEach(appendReferenced);
         }
       }
 
       appendReferenced(this);
     }
     return _transitiveFiles;
@@ skipping 387 matching lines @@
       cycle.libraries.add(node.file);
       fileToCycleMap[node.file] = cycle;
     }
     topologicallySortedCycles.add(cycle);
   }
 
   _LibraryNode getNode(FileState file) {
     return nodesOfFiles.putIfAbsent(file, () => new _LibraryNode(this, file));
   }
 }