Compute correct parent and fileUri for top-level fields.

pkg/front_end/test/fasta/function_in_field.dart

Index: pkg/front_end/test/fasta/function_in_field.dart
diff --git a/pkg/front_end/test/fasta/function_in_field.dart b/pkg/front_end/test/fasta/function_in_field.dart
new file mode 100644
index 0000000000000000000000000000000000000000..e15957964122c6271ffdafec0d33d5210da62a71
--- /dev/null
+++ b/pkg/front_end/test/fasta/function_in_field.dart
@@ -0,0 +1,12 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+var x = () {
+  var y = 42;
+  return y;
+};
+
+main() {
+  print(x());
+}