Move kernel baseline tests to front_end.

pkg/front_end/test/fasta/rasta/issue_000007.dart.dartk.expect

-library;
-import self as self;
-import "dart:core" as core;
-
-class Base extends core::Object {
-  constructor •() → self::Base
-    : super core::Object::•();
-}
-class Mixin extends core::Object {
-  constructor •() → self::Mixin
-    : super core::Object::•();
-  method foo() → dynamic
-    return core::print("foo");
-}
-class Sub extends self::Base+Mixin#0 {
-  constructor •() → self::Sub
-    : super self::Base+Mixin#0::•();
-}
-abstract class Base+Mixin#0 extends self::Base implements self::Mixin {
-  constructor •() → self::Base
-    : super self::Base::•();
-  method foo() → dynamic
-    return core::print("foo");
-}
-static method main() → dynamic {
-  new self::Sub::•().foo();
-}