Revert 12609 (Allow partial scanning of large arrays)

src/spaces.cc

Index: src/spaces.cc
===================================================================
--- src/spaces.cc	(revision 12609)
+++ src/spaces.cc	(working copy)
@@ -2678,10 +2678,12 @@
 
   HeapObject* object = page->GetObject();
 
-  // Make the object consistent so the large object space can be traversed.
+#ifdef DEBUG
+  // Make the object consistent so the heap can be vefified in OldSpaceStep.
   reinterpret_cast<Object**>(object->address())[0] =
       heap()->fixed_array_map();
   reinterpret_cast<Object**>(object->address())[1] = Smi::FromInt(0);
+#endif
 
   heap()->incremental_marking()->OldSpaceStep(object_size);
   return object;