Move DescriptorArray into the map

src/transitions.h

Index: src/transitions.h
diff --git a/src/transitions.h b/src/transitions.h
index 9643a61812b8feca8bfdc8b9dccc7fe1acc8dc72..0a660261c58735e2fe8511e2ff8903caf919bdd5 100644
--- a/src/transitions.h
+++ b/src/transitions.h
@@ -39,13 +39,22 @@ namespace internal {
 
 
 // TransitionArrays are fixed arrays used to hold map transitions for property,
-// constant, and element changes.
-// The format of the these objects is:
-// [0] Descriptor array
-// [1] Undefined or back pointer map
-// [2] Smi(0) or elements transition map
-// [3] Smi(0) or fixed array of prototype transitions
-// [4] First transition
+// constant, and element changes. They can either be simple transition arrays
+// that store a single property transition, or a full transition array that has
+// space for elements transitions, prototype transitions and multiple property
+// transitons. The details related to property transitions are accessed in the
+// descriptor array of the target map. In the case of a simple transition, the
+// key is also read from the descriptor array of the target map.
+//
+// The simple format of the these objects is:
+// [0] Undefined or back pointer map
+// [1] Single transition
+//
+// The full format is:
+// [0] Undefined or back pointer map
+// [1] Smi(0) or elements transition map
+// [2] Smi(0) or fixed array of prototype transitions
+// [3] First transition
 // [length() - kTransitionSize] Last transition
 class TransitionArray: public FixedArray {
  public:
@@ -71,10 +80,6 @@ class TransitionArray: public FixedArray {
   inline bool HasElementsTransition();
   inline void ClearElementsTransition();
 
-  inline Object** GetDescriptorsSlot();
-  inline DescriptorArray* descriptors();
-  inline void set_descriptors(DescriptorArray* descriptors);
-
   inline Object* back_pointer_storage();
   inline void set_back_pointer_storage(
       Object* back_pointer,
@@ -102,11 +107,8 @@ class TransitionArray: public FixedArray {
       SimpleTransitionFlag flag,
       String* key,
       Map* target,
-      DescriptorArray* descriptors,
       Object* back_pointer);
 
-  static MUST_USE_RESULT MaybeObject* AllocateDescriptorsHolder();
-
   MUST_USE_RESULT MaybeObject* ExtendToFullTransitionArray();
 
   // Copy the transition array, inserting a new transition.
@@ -125,7 +127,6 @@ class TransitionArray: public FixedArray {
   // Allocates a TransitionArray.
   MUST_USE_RESULT static MaybeObject* Allocate(int number_of_transitions);
 
-  bool IsDescriptorsHolder() { return length() == kDescriptorsHolderSize; }
   bool IsSimpleTransition() { return length() == kSimpleTransitionSize; }
   bool IsFullTransitionArray() { return length() >= kFirstIndex; }
 
@@ -135,24 +136,20 @@ class TransitionArray: public FixedArray {
   // Constant for denoting key was not found.
   static const int kNotFound = -1;
 
-  static const int kDescriptorsIndex = 0;
-  static const int kBackPointerStorageIndex = 1;
-  static const int kDescriptorsHolderSize = 2;
+  static const int kBackPointerStorageIndex = 0;
 
   // Layout for full transition arrays.
-  static const int kElementsTransitionIndex = 2;
-  static const int kPrototypeTransitionsIndex = 3;
-  static const int kFirstIndex = 4;
+  static const int kElementsTransitionIndex = 1;
+  static const int kPrototypeTransitionsIndex = 2;
+  static const int kFirstIndex = 3;
 
   // Layout for simple transition arrays.
-  static const int kSimpleTransitionTarget = 2;
-  static const int kSimpleTransitionSize = 3;
+  static const int kSimpleTransitionTarget = 1;
+  static const int kSimpleTransitionSize = 2;
   static const int kSimpleTransitionIndex = 0;
   STATIC_ASSERT(kSimpleTransitionIndex != kNotFound);
 
-  static const int kDescriptorsOffset = FixedArray::kHeaderSize;
-  static const int kBackPointerStorageOffset = kDescriptorsOffset +
-                                               kPointerSize;
+  static const int kBackPointerStorageOffset = FixedArray::kHeaderSize;
 
   // Layout for the full transition array header.
   static const int kElementsTransitionOffset = kBackPointerStorageOffset +