Add Object::IsNullOrUndefined(Isolate*) helper method

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index 334a6e16bfe69367c93ff8647ed3bc2c579a6d0d..fa238742d5d4f16f68f0816c850f58cc275b284a 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -1921,9 +1921,16 @@ class V8_EXPORT Value : public Data {
    */
   V8_INLINE bool IsNull() const;
 
-   /**
-   * Returns true if this value is true.
+  /**
+   * Returns true if this value is either the null or the undefined value.
+   * See ECMA-262
+   * 4.3.11. and 4.3.12
    */
+  V8_INLINE bool IsNullOrUndefined() const;
+
+  /**
+  * Returns true if this value is true.
+  */
   bool IsTrue() const;
 
   /**
@@ -2243,6 +2250,7 @@ class V8_EXPORT Value : public Data {
  private:
   V8_INLINE bool QuickIsUndefined() const;
   V8_INLINE bool QuickIsNull() const;
+  V8_INLINE bool QuickIsNullOrUndefined() const;
   V8_INLINE bool QuickIsString() const;
   bool FullIsUndefined() const;
   bool FullIsNull() const;
@@ -9144,6 +9152,23 @@ bool Value::QuickIsNull() const {
   return (I::GetOddballKind(obj) == I::kNullOddballKind);
 }
 
+bool Value::IsNullOrUndefined() const {
+#ifdef V8_ENABLE_CHECKS
+  return FullIsNull() || FullIsUndefined();
+#else
+  return QuickIsNullOrUndefined();
+#endif
+}
+
+bool Value::QuickIsNullOrUndefined() const {
+  typedef internal::Object O;
+  typedef internal::Internals I;
+  O* obj = *reinterpret_cast<O* const*>(this);
+  if (!I::HasHeapObjectTag(obj)) return false;
+  if (I::GetInstanceType(obj) != I::kOddballType) return false;
+  int kind = I::GetOddballKind(obj);
+  return kind == I::kNullOddballKind || kind == I::kUndefinedOddballKind;
+}
 
 bool Value::IsString() const {
 #ifdef V8_ENABLE_CHECKS