Lint rule: Do not override fields.

test/rules/final_override_non_final.dart

Index: test/rules/final_override_non_final.dart
diff --git a/test/rules/final_override_non_final.dart b/test/rules/final_override_non_final.dart
new file mode 100644
index 0000000000000000000000000000000000000000..775062e9fe700f0612984408c1c60c58e676df92
--- /dev/null
+++ b/test/rules/final_override_non_final.dart
@@ -0,0 +1,34 @@
+// Copyright (c) 2016, 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.
+
+// test w/ `dart test/util/solo_test.dart final_override_non_final`
+
+class Base {
+  Object field = 'lorem';
+
+  Object something = 'change';
+}
+
+class Bad extends Base {
+  @override
+  final field = 'ipsum'; // LINT
+}
+
+class Sophisticated extends Base {
+  @override
+  final field = 'ipsum'; // OK
+
+  void set field(Object newValue) {
+    
+  }
+}
+
+class Ok extends Base {
+  @override
+  Object something = 'blah'; // OK
+
+  Object newField;
+
+  final Object newFinal = 'ignore';
+}