Couple the enumeration index of a property to the size of the descriptor array where it first appea…

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index fbb0183815083b93fe410b498c968372f7f71df4..4a7f8a4a602842bb049c1b32e94945e64a9cfa8e 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -2095,6 +2095,7 @@ void DescriptorArray::Set(int descriptor_number,
                           const WhitenessWitness&) {
   // Range check.
   ASSERT(descriptor_number < number_of_descriptors());
+  ASSERT(desc->GetDetails().index() <= number_of_descriptors());
   ASSERT(desc->GetDetails().index() > 0);
 
   NoIncrementalWriteBarrierSet(this,
@@ -2109,6 +2110,16 @@ void DescriptorArray::Set(int descriptor_number,
 }
 
 
+void DescriptorArray::Append(Descriptor* desc,
+                             const WhitenessWitness& witness) {
+  int descriptor_number = NumberOfSetDescriptors();
+  int enumeration_index = descriptor_number + 1;
+  desc->SetEnumerationIndex(enumeration_index);
+  Set(descriptor_number, desc, witness);
+  SetLastAdded(descriptor_number);
+}
+
+
 void DescriptorArray::NoIncrementalWriteBarrierSwapDescriptors(
     int first, int second) {
   NoIncrementalWriteBarrierSwap(this, ToKeyIndex(first), ToKeyIndex(second));