ExtendStorageStub added, it is aimed for extending objects backing store when it runs out of space.

src/x64/interface-descriptors-x64.cc

Index: src/x64/interface-descriptors-x64.cc
diff --git a/src/x64/interface-descriptors-x64.cc b/src/x64/interface-descriptors-x64.cc
index 84fdca4fb9226d6b3ff43f2eaadf7358a5380f03..05c24ced969df4e364352db67b9c0f46520a80f0 100644
--- a/src/x64/interface-descriptors-x64.cc
+++ b/src/x64/interface-descriptors-x64.cc
@@ -29,6 +29,9 @@ const Register StoreDescriptor::NameRegister() { return rcx; }
 const Register StoreDescriptor::ValueRegister() { return rax; }
 
 
+const Register ExtendStorageDescriptor::MapRegister() { return rbx; }
+
+
 const Register ElementTransitionAndStoreDescriptor::MapRegister() {
   return rbx;
 }