Fix diet_listener.dart imports

Change-Id: Iff0b5f9eae0080f961c3b0395a65f854f4714e41
Reviewed-on: https://dart-review.googlesource.com/56326
Reviewed-by: Dmitry Stefantsov <dmitryas@google.com>
diff --git a/pkg/front_end/lib/src/fasta/source/diet_listener.dart b/pkg/front_end/lib/src/fasta/source/diet_listener.dart
index 71ae91c..b4639f1 100644
--- a/pkg/front_end/lib/src/fasta/source/diet_listener.dart
+++ b/pkg/front_end/lib/src/fasta/source/diet_listener.dart
@@ -5,8 +5,15 @@
 library fasta.diet_listener;
 
 import 'package:kernel/ast.dart'
-    show AsyncMarker, Class, InterfaceType, Typedef;
-import 'package:kernel/ast.dart';
+    show
+        AsyncMarker,
+        Class,
+        Expression,
+        InterfaceType,
+        Library,
+        LibraryDependency,
+        LibraryPart,
+        Typedef;
 
 import 'package:kernel/class_hierarchy.dart' show ClassHierarchy;