Support check mode for statics.

tests/language/compile_time_constant_checked_test.dart

+// Copyright (c) 2012, 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.
+
+final int x = 'foo'; /// 01: static type warning, dynamic type error
+const int y = 'foo'; /// 02: static type warning, compile-time error
+int z = 'foo'; /// 03: static type warning, dynamic type error
+
+main() {
+  print(x); /// 01: continued
+  print(y); /// 02: continued
+  print(z); /// 03: continued
+}