Prototype objects never share their map, and hence cannot be in deprecated state.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index ea4b6644c11c3ddda184b086a35969637533821c..7a3490286ae12379c78838aa97a7890a94a8f955 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -2931,30 +2931,7 @@ Handle<Map> Map::GeneralizeAllFieldRepresentations(
 
 
 // static
-MaybeHandle<Map> Map::TryUpdate(Handle<Map> map) {
-  Handle<Map> proto_map(map);
-  while (proto_map->prototype()->IsJSObject()) {
-    Handle<JSObject> holder(JSObject::cast(proto_map->prototype()));
-    proto_map = Handle<Map>(holder->map());
-    if (proto_map->is_deprecated() && JSObject::TryMigrateInstance(holder)) {
-      proto_map = Handle<Map>(holder->map());
-    }
-  }
-  return TryUpdateInternal(map);
-}
-
-
-// static
-Handle<Map> Map::Update(Handle<Map> map) {
-  if (!map->is_deprecated()) return map;
-  return ReconfigureProperty(map, -1, kData, NONE, Representation::None(),
-                             HeapType::None(map->GetIsolate()),
-                             ALLOW_IN_DESCRIPTOR);
-}
-
-
-// static
-MaybeHandle<Map> Map::TryUpdateInternal(Handle<Map> old_map) {
+MaybeHandle<Map> Map::TryUpdate(Handle<Map> old_map) {
   DisallowHeapAllocation no_allocation;
   DisallowDeoptimization no_deoptimization(old_map->GetIsolate());
 
@@ -3018,6 +2995,15 @@ MaybeHandle<Map> Map::TryUpdateInternal(Handle<Map> old_map) {
 }
 
 
+// static
+Handle<Map> Map::Update(Handle<Map> map) {
+  if (!map->is_deprecated()) return map;
+  return ReconfigureProperty(map, -1, kData, NONE, Representation::None(),
+                             HeapType::None(map->GetIsolate()),
+                             ALLOW_IN_DESCRIPTOR);
+}
+
+
 MaybeHandle<Object> JSObject::SetPropertyWithInterceptor(LookupIterator* it,
                                                          Handle<Object> value) {
   Handle<Name> name = it->name();