Improve fast to slow elements conversion:

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 2417c3207b3e11279bc0640f5cf97df379993754..d63d790b8a46b1eef3507f93221d90a3c40c5f31 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -1967,6 +1967,17 @@ void DescriptorArray::Swap(int first, int second) {
 
 
 template<typename Shape, typename Key>
+int HashTable<Shape, Key>::ComputeCapacity(int at_least_space_for) {
+  const int kMinCapacity = 32;
+  int capacity = RoundUpToPowerOf2(at_least_space_for * 2);
+  if (capacity < kMinCapacity) {
+    capacity = kMinCapacity;  // Guarantee min capacity.
+  }
+  return capacity;
+}
+
+
+template<typename Shape, typename Key>
 int HashTable<Shape, Key>::FindEntry(Key key) {
   return FindEntry(GetIsolate(), key);
 }