Use instance type in Object.prototype.toString().

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index d812c326297ebcf4c081af598dde69ee1da7a313..f6368981404e2ca79daf9c5e6af5322a7582efdb 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -415,6 +415,7 @@ const int kStubMinorKeyBits = kSmiValueSize - kStubMajorKeyBits - 1;
   V(JS_VALUE_TYPE)                                              \
   V(JS_DATE_TYPE)                                               \
   V(JS_OBJECT_TYPE)                                             \
+  V(JS_ARGUMENTS_TYPE)                                          \
   V(JS_CONTEXT_EXTENSION_OBJECT_TYPE)                           \
   V(JS_GENERATOR_OBJECT_TYPE)                                   \
   V(JS_MODULE_TYPE)                                             \
@@ -435,6 +436,7 @@ const int kStubMinorKeyBits = kSmiValueSize - kStubMajorKeyBits - 1;
   V(JS_WEAK_SET_TYPE)                                           \
   V(JS_PROMISE_TYPE)                                            \
   V(JS_REGEXP_TYPE)                                             \
+  V(JS_ERROR_TYPE)                                              \
                                                                 \
   V(JS_BOUND_FUNCTION_TYPE)                                     \
   V(JS_FUNCTION_TYPE)                                           \
@@ -712,6 +714,7 @@ enum InstanceType {
   // Like JS_OBJECT_TYPE, but created from API function.
   JS_API_OBJECT_TYPE,
   JS_OBJECT_TYPE,
+  JS_ARGUMENTS_TYPE,
   JS_CONTEXT_EXTENSION_OBJECT_TYPE,
   JS_GENERATOR_OBJECT_TYPE,
   JS_MODULE_TYPE,
@@ -727,6 +730,7 @@ enum InstanceType {
   JS_WEAK_SET_TYPE,
   JS_PROMISE_TYPE,
   JS_REGEXP_TYPE,
+  JS_ERROR_TYPE,
   JS_BOUND_FUNCTION_TYPE,
   JS_FUNCTION_TYPE,  // LAST_JS_OBJECT_TYPE, LAST_JS_RECEIVER_TYPE
 
@@ -1939,10 +1943,6 @@ class JSReceiver: public HeapObject {
   // Returns the class name ([[Class]] property in the specification).
   String* class_name();
 
-  // Returns the builtin string tag used in Object.prototype.toString.
-  MUST_USE_RESULT static MaybeHandle<String> BuiltinStringTag(
-      Handle<JSReceiver> object);
-
   // Returns the constructor name (the name (possibly, inferred name) of the
   // function that was used to instantiate the object).
   static Handle<String> GetConstructorName(Handle<JSReceiver> receiver);