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

pkg/analyzer/lib/src/dart/analysis/driver.dart

Index: pkg/analyzer/lib/src/dart/analysis/driver.dart
diff --git a/pkg/analyzer/lib/src/dart/analysis/driver.dart b/pkg/analyzer/lib/src/dart/analysis/driver.dart
index 543e3828d86e6b3876ee63256c3e6101796bb46d..7486496bc19c246b785ccd56d3ed82c5b6c2035f 100644
--- a/pkg/analyzer/lib/src/dart/analysis/driver.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/driver.dart
@@ -1139,7 +1139,6 @@ class _LibraryNode {
   final FileState file;
   final Uri uri;
 
-  Set<FileState> transitiveDependencies;
   String _dependencySignature;
 
   _LibraryNode(this.driver, this.file, this.uri);
@@ -1152,8 +1151,7 @@ class _LibraryNode {
       signature.addString(driver._sdkBundle.apiSignature);
 
       // Add all unlinked API signatures.
-      computeTransitiveDependencies();
-      transitiveDependencies
+      file.transitiveFiles
           .map((file) => file.apiSignature)
           .forEach(signature.addBytes);
 
@@ -1170,20 +1168,6 @@ class _LibraryNode {
     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();
 }