[turbofan] Properly implement %_ClassOf intrinsic.

src/builtins/builtins-conversion.cc

 // Copyright 2016 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.
 
 #include "src/builtins/builtins-utils.h"
 #include "src/builtins/builtins.h"
 #include "src/code-factory.h"
 #include "src/code-stub-assembler.h"
 
 namespace v8 {
@@ skipping 456 matching lines @@
   assembler.Bind(&if_noconstructor);
   assembler.TailCallRuntime(
       Runtime::kThrowUndefinedOrNullToObject, context,
       assembler.HeapConstant(
           assembler.factory()->NewStringFromAsciiChecked("ToObject", TENURED)));
 
   assembler.Bind(&if_jsreceiver);
   assembler.Return(object);
 }
 
+// Deprecated ES5 [[Class]] internal property (used to implement %_ClassOf).
+void Builtins::Generate_ClassOf(compiler::CodeAssemblerState* state) {
+  typedef compiler::Node Node;
+  typedef TypeofDescriptor Descriptor;
+  CodeStubAssembler assembler(state);
+
+  Node* object = assembler.Parameter(Descriptor::kObject);
+
+  assembler.Return(assembler.ClassOf(object));
+}
+
 // ES6 section 12.5.5 typeof operator
 void Builtins::Generate_Typeof(compiler::CodeAssemblerState* state) {
   typedef compiler::Node Node;
   typedef TypeofDescriptor Descriptor;
   CodeStubAssembler assembler(state);
 
   Node* object = assembler.Parameter(Descriptor::kObject);
   Node* context = assembler.Parameter(Descriptor::kContext);
 
   assembler.Return(assembler.Typeof(object, context));
 }
 
 }  // namespace internal
 }  // namespace v8