Work towards unifying descriptor array handling.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 199c6e58ea3409c25bb112a73c0b711171622c04..9642885f478593de515f13a45fe0fbb5c29c720d 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -3452,7 +3452,7 @@ class DescriptorArray: public FixedArray {
   inline void Set(int descriptor_number,
                   Descriptor* desc,
                   const WhitenessWitness&);
-  inline void Set(int descriptor_number, Descriptor* desc);
+  void Replace(int descriptor_number, Descriptor* descriptor);
 
   // Append automatically sets the enumeration index. This should only be used
   // to add descriptors in bulk at the end, followed by sorting the descriptor
@@ -3460,12 +3460,6 @@ class DescriptorArray: public FixedArray {
   inline void Append(Descriptor* desc, const WhitenessWitness&);
   inline void Append(Descriptor* desc);
 
-  // Transfer a complete descriptor from the src descriptor array to this
-  // descriptor array.
-  void CopyFrom(int dst_index,
-                DescriptorArray* src,
-                int src_index,
-                const WhitenessWitness&);
   static Handle<DescriptorArray> Merge(Handle<Map> left_map,
                                        int verbatim,
                                        int valid,
@@ -3481,12 +3475,14 @@ class DescriptorArray: public FixedArray {
                          DescriptorArray* other);
 
   static Handle<DescriptorArray> CopyUpTo(Handle<DescriptorArray> desc,
-                                          int enumeration_index);
+                                          int enumeration_index,
+                                          int slack = 0);
 
   static Handle<DescriptorArray> CopyUpToAddAttributes(
       Handle<DescriptorArray> desc,
       int enumeration_index,
-      PropertyAttributes attributes);
+      PropertyAttributes attributes,
+      int slack = 0);
 
   // Sort the instance descriptors by the hash codes of their keys.
   void Sort();
@@ -3589,6 +3585,14 @@ class DescriptorArray: public FixedArray {
            kDescriptorValue;
   }
 
+  // Transfer a complete descriptor from the src descriptor array to this
+  // descriptor array.
+  void CopyFrom(int index,
+                DescriptorArray* src,
+                const WhitenessWitness&);
+
+  inline void Set(int descriptor_number, Descriptor* desc);
+
   // Swap first and second descriptor.
   inline void SwapSortedKeys(int first, int second);