When reordering constructor initializers, use correct types for temp vars.

pkg/front_end/testcases/reorder_super.dart

+// Copyright (c) 2017, 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.
+
+// This test verifies that super calls get reordered properly.  It exercises the
+// case where the arguments to super have a type other than `dynamic`.
+String events = '';
+
+int f(x) {
+  events += 'f($x)\n';
+  return 0;
+}
+
+String g(x) {
+  events += 'g($x)\n';
+  return 'foo';
+}
+
+class B {
+  num x;
+  String y;
+  B(this.x, this.y) {
+    events += 'super($x, $y)\n';
+  }
+}
+
+class C extends B {
+  final z;
+  C()
+      : super(f(1), g(2)),
+        z = f(3);
+}
+
+main() {
+  new C();
+  if (events != 'f(1)\ng(2)\nf(3)\nsuper(0, foo)\n') {
+    throw 'Unexpected sequence of events: $events';
+  }
+}