Fix --gc_at_alloc

runtime/vm/raw_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/raw_object.h"
 
 #include "vm/class_table.h"
 #include "vm/freelist.h"
 #include "vm/isolate.h"
 #include "vm/object.h"
@@ skipping 233 matching lines @@
         size = RawInstance::VisitInstancePointers(raw_obj, visitor);
         break;
       }
 #undef RAW_VISITPOINTERS
       case kFreeListElement: {
         uword addr = RawObject::ToAddr(const_cast<RawObject*>(this));
         FreeListElement* element = reinterpret_cast<FreeListElement*>(addr);
         size = element->Size();
         break;
       }
+      case kNullCid:

[Ivan Posva, 2013/09/27 00:28:58]

How come we are visiting the Null object suddenly?

+        size = Size();
+        break;
       default:
         OS::Print("Class Id: %" Pd "\n", class_id);
         UNREACHABLE();
         break;
     }
   } else {
     RawInstance* raw_obj = reinterpret_cast<RawInstance*>(this);
     size = RawInstance::VisitInstancePointers(raw_obj, visitor);
   }
 
@@ skipping 538 matching lines @@
 
 intptr_t RawMirrorReference::VisitMirrorReferencePointers(
     RawMirrorReference* raw_obj, ObjectPointerVisitor* visitor) {
   // Make sure that we got here with the tagged pointer as this.
   ASSERT(raw_obj->IsHeapObject());
   visitor->VisitPointers(raw_obj->from(), raw_obj->to());
   return MirrorReference::InstanceSize();
 }
 
 }  // namespace dart