Issue 991: Missing compiler errors for uninitialized final fields

tests/language/src/ConstructorDuplicateInitializersTest.dart

+// Copyright (c) 2011, 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.
+// Check that initializers are not duplicated
+
+
+class Class {
+  Class(var v)
+    : field_ = v
+      // Test against duplicate final field initializaion in initializing list.
+    , field_ = 2  /// 01: compile-time error
+  ;
+  Class.field(this.field_)
+      // Test against duplicate final field initialization between initializing
+      // formals and initializer list.
+    : field_ = 2  /// 02: compile-time error
+  ;
+  final field_;
+}
+
+main() {
+  new Class(42);
+  new Class.field(42);
+}