Migrate tests for initializing formals

pkg/dev_compiler/test/codegen/language/initializing_formal_scope_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";
+
+// Duplicate definition checks for `this.x` will check the scopes associated
+// with the constructor, not all enclosing scopes; so this is not a conflict.
+var x;
+
+class A {
+  var x;
+  A(this.x) {
+    // In the body the field is in scope, not the initializing formal;
+    // so we can use the setter.
+    x += 1;
+  }
+}
+
+main() {
+  A a = new A(2);
+  Expect.equals(a.x, 3);
+}