fix #27421, DDC did not generate implicit super calls in some cases

pkg/dev_compiler/test/codegen/language/implicit_super_constructor_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.
 
 import "package:expect/expect.dart";
 
-class C<D> {
-  void set D(int value) {
-    field = value;
-  }
+abstract class A {
+  int _x = 42;
+}
 
-  int field;
+abstract class B extends A {}
+
+class C extends B {
+  C() {}
 }
 
 main() {
-  C<int> c = new C<int>();
-  c.D = 1;
-  Expect.equals(c.field, 1);
+  // Regression test for https://github.com/dart-lang/sdk/issues/27421
+  Expect.equals(new C()._x, 42);
 }