Move kernel baseline tests to front_end.

pkg/front_end/testcases/rasta/static.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 Foo {
   static const staticConstant = 42;
   static var staticField = 42;
   static staticFunction() {}
 
   static get staticGetter => null;
@@ skipping 68 matching lines @@
     Foo.staticFunction ??= 87;
     use(Foo.staticFunction ??= 87);
     Foo.staticGetter ??= 87;
     use(Foo.staticGetter ??= 87);
     Foo.staticSetter ??= 87;
     use(Foo.staticSetter ??= 87);
   } on NoSuchMethodError {
     // Expected.
   }
 }