Fixes for review comments.

pkg/front_end/tool/fasta_perf.dart

Index: pkg/front_end/tool/fasta_perf.dart
diff --git a/pkg/front_end/tool/fasta_perf.dart b/pkg/front_end/tool/fasta_perf.dart
index 6cfabecf6d9fdaa7945faf342711c0bdc0b263d2..7a031dada9c4e2c72d35f97901470a040078be5f 100644
--- a/pkg/front_end/tool/fasta_perf.dart
+++ b/pkg/front_end/tool/fasta_perf.dart
@@ -163,8 +163,8 @@ Set<String> extractDirectiveUris(List<int> contents) {
   var listener = new DirectiveListenerWithNative();
   new TopLevelParser(listener).parseUnit(tokenize(contents));
   return new Set<String>()
-    ..addAll(listener.imports.map((d) => d.uri))
-    ..addAll(listener.exports.map((d) => d.uri))
+    ..addAll(listener.imports.map((directive) => directive.uri))
+    ..addAll(listener.exports.map((directive) => directive.uri))
     ..addAll(listener.parts);
 }