Version 2.2.11...

src/objects-inl.h

Index: src/objects-inl.h
===================================================================
--- src/objects-inl.h	(revision 4699)
+++ src/objects-inl.h	(working copy)
@@ -1691,13 +1691,19 @@
 
 
 Object* String::TryFlatten(PretenureFlag pretenure) {
-  // We don't need to flatten strings that are already flat.  Since this code
-  // is inlined, it can be helpful in the flat case to not call out to Flatten.
-  if (IsFlat()) return this;
+  if (!StringShape(this).IsCons()) return this;
+  ConsString* cons = ConsString::cast(this);
+  if (cons->second()->length() == 0) return cons->first();
   return SlowTryFlatten(pretenure);
 }
 
 
+String* String::TryFlattenGetString(PretenureFlag pretenure) {
+  Object* flat = TryFlatten(pretenure);
+  return flat->IsFailure() ? this : String::cast(flat);
+}
+
+
 uint16_t String::Get(int index) {
   ASSERT(index >= 0 && index < length());
   switch (StringShape(this).full_representation_tag()) {