Move kernel baseline tests to front_end.

pkg/front_end/testcases/rasta/super_operator.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.md file.
 
 class A {
   operator + (String s) => null;
 
   operator [] (i) => null;
 
   operator []= (i, val) {}
 }
 
 class B extends A {
   operator + (String s) => super + ("${s}${s}");
 
   operator [] (i) => super[i];
 
   operator []= (i, val) => super[i++] += val;
 }
 
 class Autobianchi {
   g() => super[0];
 }