Swapped transition array and descriptor array.

src/transitions.h

Index: src/transitions.h
diff --git a/src/transitions.h b/src/transitions.h
index 57f32535a5a01ebd938ca80513e4ddfe86fa3ea2..b0443970f613da27fbed09f3edda71512d61ae29 100644
--- a/src/transitions.h
+++ b/src/transitions.h
@@ -63,6 +63,16 @@ class TransitionArray: public FixedArray {
   inline bool HasElementsTransition();
   inline void ClearElementsTransition();
 
+  inline DescriptorArray* descriptors();
+  inline void set_descriptors(DescriptorArray* descriptors,
+                              WriteBarrierMode mode = UPDATE_WRITE_BARRIER);
+  inline Object** GetDescriptorsSlot();
+
+  inline Object* back_pointer_storage();
+  inline void set_back_pointer_storage(
+      Object* back_pointer,
+      WriteBarrierMode mode = UPDATE_WRITE_BARRIER);
+
   inline FixedArray* GetPrototypeTransitions();
   inline void SetPrototypeTransitions(
       FixedArray* prototype_transitions,
@@ -106,15 +116,20 @@ class TransitionArray: public FixedArray {
   // Constant for denoting key was not found.
   static const int kNotFound = -1;
 
-  static const int kElementsTransitionIndex = 0;
-  static const int kPrototypeTransitionsIndex = 1;
-  static const int kFirstIndex = 2;
+  static const int kDescriptorsIndex = 0;
+  static const int kBackPointerStorageIndex = 1;
+  static const int kElementsTransitionIndex = 2;
+  static const int kPrototypeTransitionsIndex = 3;
+  static const int kFirstIndex = 4;
 
   // Layout transition array header.
-  static const int kElementsTransitionOffset = FixedArray::kHeaderSize;
+  static const int kDescriptorsOffset = FixedArray::kHeaderSize;
+  static const int kBackPointerStorageOffset = kDescriptorsOffset +
+                                               kPointerSize;
+  static const int kElementsTransitionOffset = kBackPointerStorageOffset +
+                                               kPointerSize;
   static const int kPrototypeTransitionsOffset = kElementsTransitionOffset +
                                                  kPointerSize;
-  static const int kFirstOffset = kPrototypeTransitionsOffset + kPointerSize;
 
   // Layout of map transition.
   static const int kTransitionKey = 0;