Compute and flush sets of transitively referenced files in File[System]State.

pkg/analyzer/lib/src/dart/analysis/driver.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 'dart:collection';
 import 'dart:typed_data';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/error/error.dart';
@@ skipping 1121 matching lines @@
   final _LibraryNode node;
   final SummaryDataStore store;
   _LibraryContext(this.file, this.node, this.store);
 }
 
 class _LibraryNode {
   final AnalysisDriver driver;
   final FileState file;
   final Uri uri;
 
-  Set<FileState> transitiveDependencies;
   String _dependencySignature;
 
   _LibraryNode(this.driver, this.file, this.uri);
 
   String get dependencySignature {
     return _dependencySignature ??=
         driver._dependencySignatureMap.putIfAbsent(uri, () {
       ApiSignature signature = new ApiSignature();
       signature.addUint32List(driver._salt);
       signature.addString(driver._sdkBundle.apiSignature);
 
       // Add all unlinked API signatures.
-      computeTransitiveDependencies();
-      transitiveDependencies
+      file.transitiveFiles
           .map((file) => file.apiSignature)
           .forEach(signature.addBytes);
 
       // Combine into a single hash.
       signature.addString(uri.toString());
       return signature.toHex();
     });
   }
 
   @override
   int get hashCode => uri.hashCode;
 
   bool operator ==(other) {
     return other is _LibraryNode && other.uri == uri;
   }
 
-  void computeTransitiveDependencies() {
-    if (transitiveDependencies == null) {
-      transitiveDependencies = new Set<FileState>();
-
-      void appendDependencies(FileState file) {
-        if (transitiveDependencies.add(file)) {
-          file.dependencies.forEach(appendDependencies);
-        }
-      }
-
-      appendDependencies(file);
-    }
-  }
-
   @override
   String toString() => uri.toString();
 }