Reland of Introduce instance type for transition arrays.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index f9435439666b9b641eff7e31aedcba416cac579d..26384576cc1a8bddaea8a352993e535ac0a342d5 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -61,6 +61,7 @@
   V(Map, fixed_cow_array_map, FixedCOWArrayMap)                                \
   V(Map, fixed_double_array_map, FixedDoubleArrayMap)                          \
   V(Map, weak_cell_map, WeakCellMap)                                           \
+  V(Map, transition_array_map, TransitionArrayMap)                             \
   V(Map, one_byte_string_map, OneByteStringMap)                                \
   V(Map, one_byte_internalized_string_map, OneByteInternalizedStringMap)       \
   V(Map, function_context_map, FunctionContextMap)                             \
@@ -423,6 +424,7 @@
   V(FixedCOWArrayMap)                   \
   V(FixedDoubleArrayMap)                \
   V(WeakCellMap)                        \
+  V(TransitionArrayMap)                 \
   V(NoInterceptorResultSentinel)        \
   V(HashTableMap)                       \
   V(OrderedHashTableMap)                \
@@ -882,6 +884,13 @@
   }
   Object* encountered_weak_cells() const { return encountered_weak_cells_; }
 
+  void set_encountered_transition_arrays(Object* transition_array) {
+    encountered_transition_arrays_ = transition_array;
+  }
+  Object* encountered_transition_arrays() const {
+    return encountered_transition_arrays_;
+  }
+
   // Number of mark-sweeps.
   int ms_count() const { return ms_count_; }
 
@@ -2095,6 +2104,8 @@
 
   MUST_USE_RESULT AllocationResult AllocateWeakCell(HeapObject* value);
 
+  MUST_USE_RESULT AllocationResult AllocateTransitionArray(int capacity);
+
   // Allocates a new utility object in the old generation.
   MUST_USE_RESULT AllocationResult AllocateStruct(InstanceType type);
 
@@ -2220,6 +2231,8 @@
   Object* encountered_weak_collections_;
 
   Object* encountered_weak_cells_;
+
+  Object* encountered_transition_arrays_;
 
   StoreBufferRebuilder store_buffer_rebuilder_;