Remove parent_level field of function type parameters.

runtime/lib/mirrors.cc

Index: runtime/lib/mirrors.cc
diff --git a/runtime/lib/mirrors.cc b/runtime/lib/mirrors.cc
index b64cda34ae4c088f820bf8cbdd85c096d57300bc..89d4f7b2fdab88d282c649838118d1d56190cab7 100644
--- a/runtime/lib/mirrors.cc
+++ b/runtime/lib/mirrors.cc
@@ -1471,8 +1471,12 @@ DEFINE_NATIVE_ENTRY(ClosureMirror_function, 1) {
 
     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);