Remove unnecessary contexts in closure conversion

pkg/kernel/testcases/closures/contexts_in_super_initializers.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.
+
+// The purpose of this test is to detect that no unnecessary contexts are
+// created when a constructor parameter is used in its super initializer.  No
+// contexts should be created either in the initializer list or in the
+// constructor body.
+
+class X {}
+
+class Y {}
+
+class A {
+  X x;
+  Y y;
+  A(this.x, this.y);
+}
+
+class B extends A {
+  B(X x, Y y) : super(x, y) {}
+}
+
+main() {
+  B b = new B(new X(), new Y());
+}