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

src/objects.h

 // 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.
 
 #ifndef V8_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 
 #include "src/assert-scope.h"
@@ skipping 953 matching lines @@
   V(StringWrapper)               \
   V(Foreign)                     \
   V(Boolean)                     \
   V(JSArray)                     \
   V(JSArrayBuffer)               \
   V(JSArrayBufferView)           \
   V(JSTypedArray)                \
   V(JSDataView)                  \
   V(JSProxy)                     \
   V(JSError)                     \
+  V(JSPromise)                   \
   V(JSSet)                       \
   V(JSMap)                       \
   V(JSSetIterator)               \
   V(JSMapIterator)               \
   V(JSWeakCollection)            \
   V(JSWeakMap)                   \
   V(JSWeakSet)                   \
   V(JSRegExp)                    \
   V(HashTable)                   \
   V(Dictionary)                  \
@@ skipping 90 matching lines @@
 
   // ES6, section 7.2.2 IsArray.  NOT to be confused with %_IsArray.
   MUST_USE_RESULT static Maybe<bool> IsArray(Handle<Object> object);
 
   INLINE(bool IsNameDictionary() const);
   INLINE(bool IsGlobalDictionary() const);
   INLINE(bool IsSeededNumberDictionary() const);
   INLINE(bool IsUnseededNumberDictionary() const);
   INLINE(bool IsOrderedHashSet() const);
   INLINE(bool IsOrderedHashMap() const);
-  static bool IsPromise(Handle<Object> object);
 
   // Extract the number.
   inline double Number() const;
   INLINE(bool IsNaN() const);
   INLINE(bool IsMinusZero() const);
   bool ToInt32(int32_t* value);
   inline bool ToUint32(uint32_t* value);
 
   inline Representation OptimalRepresentation();
 
@@ skipping 9732 matching lines @@
     }
     return value;
   }
 };
 
 
 }  // NOLINT, false-positive due to second-order macros.
 }  // NOLINT, false-positive due to second-order macros.
 
 #endif  // V8_OBJECTS_H_