- Add a size field to the header.

vm/assembler_macros_ia32.cc

 // Copyright (c) 2011, 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/globals.h"
 #if defined(TARGET_ARCH_IA32)
 
 #include "vm/assembler_macros.h"
 
 #include "vm/assembler.h"
@@ skipping 29 matching lines @@
     __ cmpl(instance_reg, Address::Absolute(heap->EndAddress()));
     __ j(ABOVE_EQUAL, failure, Assembler::kNearJump);
     // Successfully allocated the object, now update top to point to
     // next object start and store the class in the class field of object.
     __ movl(Address::Absolute(heap->TopAddress()), instance_reg);
     ASSERT(instance_size >= kHeapObjectTag);
     __ subl(instance_reg, Immediate(instance_size - kHeapObjectTag));
     __ StoreIntoObject(instance_reg,
                        FieldAddress(instance_reg, Instance::class_offset()),
                        class_reg);
+    __ movl(FieldAddress(instance_reg, Object::tags_offset()),
+            Immediate(RawObject::SizeTag::encode(instance_size)));
   } else {
     __ jmp(failure);
   }
 }
 
 #undef __
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_IA32