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

src/objects-inl.h

 // Copyright 2012 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.
 //
 // Review notes:
 //
 // - The use of macros in these inline functions may seem superfluous
 // but it is absolutely needed to make sure gcc generates optimal
 // code. gcc is not happy when attempting to inline too deep.
 //
@@ skipping 773 matching lines @@
 TYPE_CHECKER(Oddball, ODDBALL_TYPE)
 TYPE_CHECKER(Cell, CELL_TYPE)
 TYPE_CHECKER(PropertyCell, PROPERTY_CELL_TYPE)
 TYPE_CHECKER(WeakCell, WEAK_CELL_TYPE)
 TYPE_CHECKER(SharedFunctionInfo, SHARED_FUNCTION_INFO_TYPE)
 TYPE_CHECKER(JSDate, JS_DATE_TYPE)
 TYPE_CHECKER(JSError, JS_ERROR_TYPE)
 TYPE_CHECKER(JSGeneratorObject, JS_GENERATOR_OBJECT_TYPE)
 TYPE_CHECKER(JSMessageObject, JS_MESSAGE_OBJECT_TYPE)
 TYPE_CHECKER(JSModule, JS_MODULE_TYPE)
+TYPE_CHECKER(JSPromise, JS_PROMISE_TYPE)
 TYPE_CHECKER(JSValue, JS_VALUE_TYPE)
 
 bool HeapObject::IsAbstractCode() const {
   return IsBytecodeArray() || IsCode();
 }
 
 bool HeapObject::IsStringWrapper() const {
   return IsJSValue() && JSValue::cast(this)->value()->IsString();
 }
 
@@ skipping 7153 matching lines @@
 #undef WRITE_INT64_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 #undef NOBARRIER_READ_BYTE_FIELD
 #undef NOBARRIER_WRITE_BYTE_FIELD
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_OBJECTS_INL_H_