Move kernel baseline tests to front_end.

pkg/front_end/testcases/argument.dart

 abstract class Base {}
 
 class Foo extends Base {}
 
 class Bar extends Base {}
 
 class Baz extends Base {}
 
 void foo(x) {}
 
 void bar(x) {}
 
 void foo_escaped(x) {}
 
 void bar_escaped(x) {}
 
 void escape(fn) {
   fn(new Baz());
 }
 
 main() {
   foo(new Foo());
   bar(new Bar());
   escape(foo_escaped);
   escape(bar_escaped);
 }