Move kernel baseline tests to front_end.

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

-library;
-import self as self;
-import "dart:core" as core;
-
-class Base extends core::Object {
-  constructor •() → void
-    ;
-}
-class Mixin extends core::Object {
-  constructor •() → void
-    ;
-  method foo() → dynamic
-    ;
-}
-class Sub extends self::Base&Mixin {
-  constructor •() → void
-    ;
-}
-abstract class Base&Mixin = self::Base with self::Mixin {
-}
-static method main() → dynamic
-  ;