Remove parent_level field of function type parameters.

runtime/lib/mirrors.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "lib/mirrors.h"
 
 #include "lib/invocation_mirror.h"
 #include "vm/bootstrap_natives.h"
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
@@ skipping 1453 matching lines @@
     if (function.IsImplicitClosureFunction()) {
       // The VM uses separate Functions for tear-offs, but the mirrors consider
       // the tear-offs to be the same as the torn-off methods. Avoid handing out
       // a reference to the tear-off here to avoid a special case in the
       // the equality test.
       function = function.parent_function();
     }
 
     Type& instantiator = Type::Handle();
     if (closure.IsClosure()) {
-      const TypeArguments& arguments =
-          TypeArguments::Handle(Closure::Cast(closure).instantiator());
+      const TypeArguments& arguments = TypeArguments::Handle(
+          Closure::Cast(closure).instantiator_type_arguments());
+      // TODO(regis): Mirrors need work to properly support generic functions.
+      // The 'instantiator' created below should not be a type, but two type
+      // argument vectors: instantiator_type_arguments and
+      // function_type_arguments.

[rmacnak, 2017/04/15 01:00:50]

Hm, that'll be annoying because type vectors are not instances. I'm content to
keep dropping function type parameters here until someone complains.

[regis, 2017/04/17 15:49:38]

I also thought it is not high priority right now. Once someone complains, I
guess we can add another fake type holding the function type arguments.

       const Class& cls =
           Class::Handle(Isolate::Current()->object_store()->object_class());
       instantiator = Type::New(cls, arguments, TokenPosition::kNoSource);
       instantiator.SetIsFinalized();
     }
     return CreateMethodMirror(function, Instance::null_instance(),
                               instantiator);
   }
   return Instance::null();
 }
@@ skipping 611 matching lines @@
 
 DEFINE_NATIVE_ENTRY(TypeMirror_subtypeTest, 2) {
   GET_NON_NULL_NATIVE_ARGUMENT(AbstractType, a, arguments->NativeArgAt(0));
   GET_NON_NULL_NATIVE_ARGUMENT(AbstractType, b, arguments->NativeArgAt(1));
   return Bool::Get(a.IsSubtypeOf(b, NULL, NULL, Heap::kNew)).raw();
 }
 
 #endif  // !PRODUCT && !DART_PRECOMPILED_RUNTIME
 
 }  // namespace dart