Add export dependencies to Kernel libraries and use them to resynthesize ExportElement(s) in Analyz…

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

Index: pkg/front_end/lib/src/fasta/builder/prefix_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/builder/prefix_builder.dart b/pkg/front_end/lib/src/fasta/builder/prefix_builder.dart
index 38c54c82ef13e3c1ba493d4a126de508ff409520..1bf253fe096f4e339473006246f90de3fea5f0fd 100644
--- a/pkg/front_end/lib/src/fasta/builder/prefix_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/prefix_builder.dart
@@ -9,7 +9,7 @@ import 'builder.dart' show Builder, LibraryBuilder, Scope;
 class PrefixBuilder extends Builder {
   final String name;
 
-  final Scope exports = new Scope.top();
+  final Scope exportScope = new Scope.top();
 
   final LibraryBuilder parent;
 
@@ -24,7 +24,7 @@ class PrefixBuilder extends Builder {
         super(parent, charOffset, parent.fileUri);
 
   Builder lookup(String name, int charOffset, Uri fileUri) {
-    return exports.lookup(name, charOffset, fileUri);
+    return exportScope.lookup(name, charOffset, fileUri);
   }
 
   @override