Introduce instance type for transition arrays.

src/transitions.h

Index: src/transitions.h
diff --git a/src/transitions.h b/src/transitions.h
index 4cac2ff3da79a1618704e3ca90228ca59aa70582..deda90ad6030786964d2753523b5351a24368df0 100644
--- a/src/transitions.h
+++ b/src/transitions.h
@@ -165,8 +165,11 @@ class TransitionArray: public FixedArray {
 
   static int Capacity(Object* raw_transitions);
 
-  // Casting.
-  static inline TransitionArray* cast(Object* obj);
+  inline static TransitionArray* cast(Object* object);
+
+  // This field should be used only by GC.
+  inline void set_next_link(Object* next, WriteBarrierMode mode);
+  inline Object* next_link();
 
   static const int kTransitionSize = 2;
   static const int kProtoTransitionHeaderSize = 1;
@@ -180,6 +183,14 @@ class TransitionArray: public FixedArray {
                                bool print_header = true);  // NOLINT
 #endif
 
+#ifdef OBJECT_PRINT
+  void TransitionArrayPrint(std::ostream& os);  // NOLINT
+#endif
+
+#ifdef VERIFY_HEAP
+  void TransitionArrayVerify();
+#endif
+
 #ifdef DEBUG
   bool IsSortedNoDuplicates(int valid_entries = -1);
   static bool IsSortedNoDuplicates(Map* map);
@@ -199,9 +210,10 @@ class TransitionArray: public FixedArray {
 
  private:
   // Layout for full transition arrays.
-  static const int kPrototypeTransitionsIndex = 0;
-  static const int kTransitionLengthIndex = 1;
-  static const int kFirstIndex = 2;
+  static const int kNextLinkIndex = 0;
+  static const int kPrototypeTransitionsIndex = 1;
+  static const int kTransitionLengthIndex = 2;
+  static const int kFirstIndex = 3;
 
   // Layout of map transition entries in full transition arrays.
   static const int kTransitionKey = 0;
@@ -304,6 +316,7 @@ class TransitionArray: public FixedArray {
                                                TransitionArray* old_transitions,
                                                Object* transitions);
 #endif
+  static void ZapTransitionArray(TransitionArray* transitions);
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(TransitionArray);
 };