Copy-on-write arrays.

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index 93b90b1846acbab3717e0ffc61c195dc06079bba..9596a6a23dc09e368b193ba0bb9849bccb3b6553 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -55,6 +55,7 @@ namespace internal {
   V(Map, heap_number_map, HeapNumberMap)                                       \
   V(Map, global_context_map, GlobalContextMap)                                 \
   V(Map, fixed_array_map, FixedArrayMap)                                       \
+  V(Map, fixed_cow_array_map, FixedCOWArrayMap)                                \
   V(Object, no_interceptor_result_sentinel, NoInterceptorResultSentinel)       \
   V(Map, meta_map, MetaMap)                                                    \
   V(Object, termination_exception, TerminationException)                       \