[turbofan] Properly implement %_ClassOf intrinsic.

src/code-stub-assembler.h

Index: src/code-stub-assembler.h
diff --git a/src/code-stub-assembler.h b/src/code-stub-assembler.h
index 5d1a5378563214c64ad5847c3964c4255a915913..db16ab4dd73c78fa9255b2ab5ef561a3ff42fc05 100644
--- a/src/code-stub-assembler.h
+++ b/src/code-stub-assembler.h
@@ -1139,6 +1139,8 @@ class V8_EXPORT_PRIVATE CodeStubAssembler : public compiler::CodeAssembler {
       Runtime::FunctionId fallback_runtime_function_id = Runtime::kHasProperty);
   Node* ForInFilter(Node* key, Node* object, Node* context);
 
+  Node* ClassOf(Node* object);
+
   Node* Typeof(Node* value, Node* context);
 
   Node* GetSuperConstructor(Node* value, Node* context);