Use the instance type to determine if an object is a promise.

src/objects.cc

 // 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.
 
 #include "src/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <sstream>
 
@@ skipping 652 matching lines @@
           MessageTemplate::kProxyRevoked,
           isolate->factory()->NewStringFromAsciiChecked("IsArray")));
       return Nothing<bool>();
     }
     return Object::IsArray(handle(proxy->target(), isolate));
   }
   return Just(false);
 }
 
 
-bool Object::IsPromise(Handle<Object> object) {
-  if (!object->IsJSObject()) return false;
-  auto js_object = Handle<JSObject>::cast(object);
-  // Promises can't have access checks.
-  if (js_object->map()->is_access_check_needed()) return false;
-  auto isolate = js_object->GetIsolate();
-  // TODO(dcarney): this should just be read from the symbol registry so as not
-  // to be context dependent.
-  auto key = isolate->factory()->promise_state_symbol();
-  // Shouldn't be possible to throw here.
-  return JSObject::HasRealNamedProperty(js_object, key).FromJust();
-}
-
-
 // static
 MaybeHandle<Object> Object::GetMethod(Handle<JSReceiver> receiver,
                                       Handle<Name> name) {
   Handle<Object> func;
   Isolate* isolate = receiver->GetIsolate();
   ASSIGN_RETURN_ON_EXCEPTION(isolate, func,
                              JSReceiver::GetProperty(receiver, name), Object);
   if (func->IsNull(isolate) || func->IsUndefined(isolate)) {
     return isolate->factory()->undefined_value();
   }
@@ skipping 18178 matching lines @@
   } else {
     // Old-style generators.
     int offset = continuation();
     CHECK(0 <= offset && offset < function()->code()->instruction_size());
     return function()->code()->SourcePosition(offset);
   }
 }
 
 }  // namespace internal
 }  // namespace v8