Ensure slow properties for simple {__proto__:null} literals.

src/ast/ast.h

Index: src/ast/ast.h
diff --git a/src/ast/ast.h b/src/ast/ast.h
index c3790b34b377fe448289a171d066207cdb8e998e..89bf0428a891d266ff4e28d0011cbed9c16d9ef7 100644
--- a/src/ast/ast.h
+++ b/src/ast/ast.h
@@ -1353,6 +1353,11 @@ class ObjectLiteralProperty final : public LiteralProperty {
 
   void set_receiver_type(Handle<Map> map) { receiver_type_ = map; }
 
+  bool IsNullPrototype() const {
+    return IsPrototype() && value()->IsNullLiteral();
+  }
+  bool IsPrototype() const { return kind() == PROTOTYPE; }
+
  private:
   friend class AstNodeFactory;
 
@@ -1390,7 +1395,13 @@ class ObjectLiteral final : public MaterializedLiteral {
   bool has_rest_property() const {
     return HasRestPropertyField::decode(bit_field_);
   }
-
+  bool HasNullPrototype() const {
+    for (int i = 0; i < properties()->length(); i++) {
+      const ObjectLiteral::Property* property = properties()->at(i);
+      if (property->IsNullPrototype()) return true;
+    }
+    return false;
+  }
   // Decide if a property should be in the object boilerplate.
   static bool IsBoilerplateProperty(Property* property);
 
@@ -1420,12 +1431,9 @@ class ObjectLiteral final : public MaterializedLiteral {
   // Assemble bitfield of flags for the CreateObjectLiteral helper.
   int ComputeFlags(bool disable_mementos = false) const {
     int flags = fast_elements() ? kFastElements : kNoFlags;
-    if (has_shallow_properties()) {
-      flags |= kShallowProperties;
-    }
-    if (disable_mementos) {
-      flags |= kDisableMementos;
-    }
+    if (HasNullPrototype()) flags |= kHasNullPrototype;
+    if (has_shallow_properties()) flags |= kShallowProperties;
+    if (disable_mementos) flags |= kDisableMementos;
     return flags;
   }
 
@@ -1435,6 +1443,7 @@ class ObjectLiteral final : public MaterializedLiteral {
     kShallowProperties = 1 << 1,
     kDisableMementos = 1 << 2,
     kHasRestProperty = 1 << 3,
+    kHasNullPrototype = 1 << 4,
   };
 
   struct Accessors: public ZoneObject {