Keep prototype maps in dictionary mode until ICs see them

src/ic/ic.cc

Index: src/ic/ic.cc
diff --git a/src/ic/ic.cc b/src/ic/ic.cc
index 8036a6ede1d6618e07235f0e2dcb2ea6ba491971..bf6768d69c305e15f330a4bcb0dfaef4a060a28b 100644
--- a/src/ic/ic.cc
+++ b/src/ic/ic.cc
@@ -223,7 +223,6 @@ bool IC::AddressIsOptimizedCode() const {
   return host->kind() == Code::OPTIMIZED_FUNCTION;
 }
 
-
 static void LookupForRead(LookupIterator* it) {
   for (; it->IsFound(); it->Next()) {
     switch (it->state()) {
@@ -641,6 +640,10 @@ MaybeHandle<Object> LoadIC::Load(Handle<Object> object, Handle<Name> name) {
     }
   }
 
+  if (state() != UNINITIALIZED) {
+    JSObject::MakePrototypesFast(object, true /* include_receiver */,
+                                 isolate());
+  }
   // Named lookup in the object.
   LookupIterator it(object, name);
   LookupForRead(&it);
@@ -1530,6 +1533,10 @@ MaybeHandle<Object> StoreIC::Store(Handle<Object> object, Handle<Name> name,
     return TypeError(MessageTemplate::kNonObjectPropertyStore, object, name);
   }
 
+  if (state() != UNINITIALIZED) {
+    JSObject::MakePrototypesFast(object, false /* include_receiver */,
+                                 isolate());
+  }
   LookupIterator it(object, name);
   if (FLAG_use_ic) UpdateCaches(&it, value, store_mode);