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

src/ast/compile-time-value.h

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_AST_COMPILE_TIME_VALUE
 #define V8_AST_COMPILE_TIME_VALUE
 
 #include "src/allocation.h"
 #include "src/globals.h"
 
 namespace v8 {
 namespace internal {
 
 class Expression;
 
 // Support for handling complex values (array and object literals) that
 // can be fully handled at compile time.
 class CompileTimeValue : public AllStatic {
  public:
-  enum LiteralType {
-    OBJECT_LITERAL_FAST_ELEMENTS,
-    OBJECT_LITERAL_SLOW_ELEMENTS,
-    ARRAY_LITERAL
-  };
+  // This is a special marker used to encode array literals. The value has to be
+  // different from any value possibly returned by
+  // ObjectLiteral::EncodeLiteralType.
+  static const int kArrayLiteralFlag = -1;
 
   static bool IsCompileTimeValue(Expression* expression);
 
   // Get the value as a compile time value.
   static Handle<FixedArray> GetValue(Isolate* isolate, Expression* expression);
 
-  // Get the type of a compile time value returned by GetValue().
-  static LiteralType GetLiteralType(Handle<FixedArray> value);
+  // Get the encoded literal type. This can either be kArrayLiteralFlag or
+  // encoded properties of an ObjectLiteral returned by
+  // ObjectLiteral::EncodeLiteralType.
+  static int GetLiteralTypeFlags(Handle<FixedArray> value);
 
   // Get the elements of a compile time value returned by GetValue().
   static Handle<HeapObject> GetElements(Handle<FixedArray> value);
 
  private:
   static const int kLiteralTypeSlot = 0;
   static const int kElementsSlot = 1;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_AST_COMPILE_TIME_VALUE