JSArray can go slow case during String.split. Guard against

src/objects-debug.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 239 matching lines @@
 
 
 void JSObject::JSObjectVerify() {
   VerifyHeapPointer(properties());
   VerifyHeapPointer(elements());
   if (HasFastProperties()) {
     CHECK_EQ(map()->unused_property_fields(),
              (map()->inobject_properties() + properties()->length() -
               map()->NextFreePropertyIndex()));
   }
-  ASSERT(map()->has_fast_elements() ==
-         (elements()->map() == GetHeap()->fixed_array_map() ||
-          elements()->map() == GetHeap()->fixed_cow_array_map()));
+  ASSERT_EQ(map()->has_fast_elements(),
+            (elements()->map() == GetHeap()->fixed_array_map() ||
+             elements()->map() == GetHeap()->fixed_cow_array_map()));
   ASSERT(map()->has_fast_elements() == HasFastElements());
 }
 
 
 void Map::MapVerify() {
   ASSERT(!HEAP->InNewSpace(this));
   ASSERT(FIRST_TYPE <= instance_type() && instance_type() <= LAST_TYPE);
   ASSERT(instance_size() == kVariableSizeSentinel ||
          (kPointerSize <= instance_size() &&
           instance_size() < HEAP->Capacity()));
@@ skipping 523 matching lines @@
         ASSERT(e->IsUndefined());
       }
     }
   }
 }
 
 
 #endif  // DEBUG
 
 } }  // namespace v8::internal