Add Null class to dart:core.

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index a6d736467d40e9e35e871ef894f485016f7d9485..d8e002686aeb36cdf5fc678c9f70718100277a2c 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -413,8 +413,7 @@ void Object::InitOnce() {
 
   // Allocate and initialize the null class.
   cls = Class::New<Instance>(kNullCid);
-  cls.set_is_finalized();
-  cls.set_is_type_finalized();
+  cls.set_is_prefinalized();
   isolate->object_store()->set_null_class(cls);
 
   // Allocate and initialize the free list element class.
@@ -841,18 +840,10 @@ RawError* Object::Init(Isolate* isolate) {
   pending_classes.Add(cls, Heap::kOld);
 
   cls = Class::New<Instance>(kNullCid);
-  cls.set_name(Symbols::Null());
-  // We immediately mark Null as finalized because it has no corresponding
-  // source.
-  cls.set_is_finalized();
-  cls.set_is_type_finalized();
   object_store->set_null_class(cls);
-  cls.set_library(core_lib);  // A sort of fiction for the mirrors.
-  // When/if we promote Null to an ordinary class, it should be added to the
-  // core library, given source and added to the list of classes pending
-  // finalization.
-  // RegisterClass(cls, Symbols::Null(), core_lib);
-  // pending_classes.Add(cls, Heap::kOld);
+  cls.set_is_prefinalized();
+  RegisterClass(cls, Symbols::Null(), core_lib);
+  pending_classes.Add(cls, Heap::kOld);
 
   cls = object_store->array_class();  // Was allocated above.
   RegisterPrivateClass(cls, Symbols::ObjectArray(), core_lib);