Make sure to flatten names before lookup. Lookup using cons strings is really slow.

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 2a74bf2d856296b2f93f5c61e023253f9ccfbb18..c3ee543b7c4e8c6666257688cef2d5db5be1229d 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -3226,6 +3226,12 @@ Handle<String> String::Flatten(Handle<String> string, PretenureFlag pretenure) {
 }
 
 
+Handle<Name> Name::Flatten(Handle<Name> name, PretenureFlag pretenure) {
+  if (name->IsSymbol()) return name;
+  return String::Flatten(Handle<String>::cast(name));
+}
+
+
 uint16_t String::Get(int index) {
   DCHECK(index >= 0 && index < length());
   switch (StringShape(this).full_representation_tag()) {