Rewrite negative const tests into a few multi tests.

tests/language/src/ConstInit6NegativeTest.dart

Index: tests/language/src/ConstInit6NegativeTest.dart
diff --git a/tests/language/src/ConstInit6NegativeTest.dart b/tests/language/src/ConstInit6NegativeTest.dart
deleted file mode 100644
index c931087fc4ddb8c641a80c20ea59503c63e2113f..0000000000000000000000000000000000000000
--- a/tests/language/src/ConstInit6NegativeTest.dart
+++ /dev/null
@@ -1,14 +0,0 @@
-// 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 initializer is expected after final variable declaration.
-
-class ConstInit6NegativeTest {
-  final x;
-  const ConstInit6NegativeTest()
-    : x = 1.toString();  // Error: not a compile time const.
-}
-
-main() {
-  const ConstInit6NegativeTest();
-}