Migrate tests for initializing formals

pkg/dev_compiler/test/codegen/language/initializing_formal_promotion_test.dart

+// 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.
+//
+// DartOptions=--initializing-formal-access
+// VMOptions=--initializing-formal-access
+
+import "package:expect/expect.dart";
+
+class B {}
+
+class A {
+  B x, y;
+  // Promotion occurs for the initializing formal because C <: B.
+  A(this.x) : y = (x is C) ? x.x : x;
+}
+
+class C extends A implements B {
+  C(B x) : super(x);
+}
+
+main() {
+  C c = new C(null);
+  C cc = new C(c);
+  Expect.equals(c.y, null);
+  Expect.equals(cc.y, null);
+}