Preserve order of fields when doing slow-to-fast object migration.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 103e93e8c4ac2547bea8167c190803000071ea6a..57fc05c82c9dc9745b8b2dcb23994a8f6ede6563 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -3582,6 +3582,11 @@ class Dictionary: public HashTable<Derived, Shape, Key> {
       Handle<Object> value,
       PropertyDetails details);
 
+  // Returns iteration indices array for the |dictionary|.
+  // Values are direct indices in the |HashTable| array.
+  static Handle<FixedArray> BuildIterationIndicesArray(
+      Handle<Derived> dictionary);
+
  protected:
   // Generic at put operation.
   MUST_USE_RESULT static Handle<Derived> AtPut(
@@ -3598,7 +3603,9 @@ class Dictionary: public HashTable<Derived, Shape, Key> {
       uint32_t hash);
 
   // Generate new enumeration indices to avoid enumeration index overflow.
-  static void GenerateNewEnumerationIndices(Handle<Derived> dictionary);
+  // Returns iteration indices array for the |dictionary|.
+  static Handle<FixedArray> GenerateNewEnumerationIndices(
+      Handle<Derived> dictionary);
   static const int kMaxNumberKeyIndex = DerivedHashTable::kPrefixStartIndex;
   static const int kNextEnumerationIndexIndex = kMaxNumberKeyIndex + 1;
 };
@@ -3627,7 +3634,7 @@ class NameDictionary: public Dictionary<NameDictionary,
 
   // Copies enumerable keys to preallocated fixed array.
   void CopyEnumKeysTo(FixedArray* storage);
-  inline static void DoGenerateNewEnumerationIndices(
+  inline static Handle<FixedArray> DoGenerateNewEnumerationIndices(
       Handle<NameDictionary> dictionary);
 
   // Find entry for key, otherwise return kNotFound. Optimized version of