Fix a pair of issues in the Dart code for the front end.

pkg/front_end/lib/src/fasta/fasta.dart

Index: pkg/front_end/lib/src/fasta/fasta.dart
diff --git a/pkg/front_end/lib/src/fasta/fasta.dart b/pkg/front_end/lib/src/fasta/fasta.dart
index 66b7ff8bb41bf811e32aa750ae52323f027ee35e..a09e53d53f10734e7fa875548ef42900081c97c3 100644
--- a/pkg/front_end/lib/src/fasta/fasta.dart
+++ b/pkg/front_end/lib/src/fasta/fasta.dart
@@ -13,7 +13,7 @@ import 'dart:io' show BytesBuilder, Directory, File, exitCode;
 import 'package:kernel/binary/ast_to_binary.dart'
     show LibraryFilteringBinaryPrinter;
 
-import 'package:kernel/kernel.dart' show Program;
+import 'package:kernel/kernel.dart' show Program, Library;
 
 import 'package:kernel/target/targets.dart' show Target, TargetFlags, getTarget;