Implement generic function type syntax in the VM (fixes #27966).

runtime/vm/class_finalizer.cc

Index: runtime/vm/class_finalizer.cc
diff --git a/runtime/vm/class_finalizer.cc b/runtime/vm/class_finalizer.cc
index c319f1f18c42b75239ae97e4b544a5692e6e2d02..c2d096917249f067afb505c8db985f5fc210266c 100644
--- a/runtime/vm/class_finalizer.cc
+++ b/runtime/vm/class_finalizer.cc
@@ -582,6 +582,16 @@ void ClassFinalizer::ResolveType(const Class& cls, const AbstractType& type) {
         if (!scope_class.IsTypedefClass()) {
           signature.set_owner(Object::Handle());
           signature.set_token_pos(TokenPosition::kNoSource);
+          if ((type.arguments() != TypeArguments::null()) &&
+              signature.HasInstantiatedSignature()) {
+            ASSERT(scope_class.IsGeneric());
+            // Although the scope class of this function type is generic,
+            // the signature of this function type does not refer to any
+            // of its type parameters. Reset its scope class to _Closure.
+            Type::Cast(type).set_type_class(Class::Handle(
+                Isolate::Current()->object_store()->closure_class()));
+            type.set_arguments(Object::null_type_arguments());
+          }
         }
       }
     }
@@ -706,7 +716,7 @@ intptr_t ClassFinalizer::ExpandAndFinalizeTypeArguments(
 
   // If we are not reifying types, drop type arguments.
   if (!FLAG_reify) {
-    type.set_arguments(TypeArguments::Handle(zone, TypeArguments::null()));
+    type.set_arguments(Object::null_type_arguments());
   }
 
   // Initialize the type argument vector.