Move kernel baseline tests to front_end.

pkg/front_end/testcases/classes.dart.outline.expect

 library;
 import self as self;
 import "dart:core" as core;
 
 class A extends core::Object {
   final field core::int x;
   final field core::int y;
   constructor •(dynamic y) → void
     ;
   method method() → dynamic
     ;
 }
 class B extends self::A {
   constructor •(dynamic x) → void
     ;
   method method() → dynamic
     ;
 }
 static method main() → dynamic
   ;