Fix comment about super type of Object class.

runtime/vm/object.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 "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 1601 matching lines @@
   do {
     if (cls.IsSignatureClass()) {
       const Function& signature_fun =
           Function::Handle(isolate, cls.signature_function());
       if (!signature_fun.is_static() &&
           !signature_fun.HasInstantiatedSignature()) {
         cls = signature_fun.Owner();
       }
     }
     num_type_args += cls.NumTypeParameters();
-    // Object is its own super class during bootstrap.
+    // Super type of Object class is null.
     if (cls.super_type() == AbstractType::null() ||
         cls.super_type() == isolate->object_store()->object_type()) {
       break;
     }
     cls = cls.SuperClass();
   } while (true);
   return num_type_args;
 }
 
 
@@ skipping 11764 matching lines @@
                                     space);
   return reinterpret_cast<RawWeakProperty*>(raw);
 }
 
 
 const char* WeakProperty::ToCString() const {
   return "_WeakProperty";
 }
 
 }  // namespace dart