Move kernel baseline tests to front_end.

pkg/front_end/test/fasta/rasta/mixin_library.dart.dartk.expect

-library test.mixin_library;
-import self as self;
-import "dart:core" as core;
-
-class Mixin<T extends core::Object> extends core::Object {
-  field dynamic x;
-  field dynamic y;
-  field dynamic z;
-  field self::Mixin::T t;
-  constructor •() → self::Mixin<self::Mixin::T>
-    : self::Mixin::x = self::f(), super core::Object::•();
-  method foo() → dynamic
-    return (throw core::_unresolvedSuperMethodError(this, #foo, <dynamic>[], <dynamic, dynamic>{}, null)).+(self::f());
-  method g(self::Mixin::T a) → self::Mixin::T
-    return null;
-  method h() → dynamic
-    return self::V();
-  method l() → dynamic
-    return self::_private();
-  method _privateMethod() → dynamic
-    return 49;
-  method publicMethod() → dynamic
-    return this._privateMethod();
-}
-static method f() → dynamic
-  return 2;
-static method V() → dynamic
-  return 87;
-static method _private() → dynamic
-  return 117;
-static method foo(dynamic m) → dynamic
-  return m._privateMethod();