Work around a bug in Clang that optimizes away a NULL check

src/spaces.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 693 matching lines @@
                                      object_size,
                                      executable,
                                      owner);
   if (chunk == NULL) return NULL;
   return LargePage::Initialize(isolate_->heap(), chunk);
 }
 
 
 void MemoryAllocator::Free(MemoryChunk* chunk) {
   LOG(isolate_, DeleteEvent("MemoryChunk", chunk));
-  if (chunk->owner() != NULL) {
+  if (chunk->has_owner()) {
     ObjectSpace space =
         static_cast<ObjectSpace>(1 << chunk->owner()->identity());
     PerformAllocationCallback(space, kAllocationActionFree, chunk->size());
   }
 
   isolate_->heap()->RememberUnmappedPage(
       reinterpret_cast<Address>(chunk), chunk->IsEvacuationCandidate());
 
   delete chunk->slots_buffer();
   delete chunk->skip_list();
@@ skipping 2424 matching lines @@
     object->ShortPrint();
     PrintF("\n");
   }
   printf(" --------------------------------------\n");
   printf(" Marked: %x, LiveCount: %x\n", mark_size, LiveBytes());
 }
 
 #endif  // DEBUG
 
 } }  // namespace v8::internal