Handle CALLBACKS correctly in IsProperty functions.

src/property.h

Index: src/property.h
diff --git a/src/property.h b/src/property.h
index d5efb7f35193f9a5ee36dbe9339e968996aaf4d0..9235c3287dc74a302fb61276d3352c6f4587f2d9 100644
--- a/src/property.h
+++ b/src/property.h
@@ -164,6 +164,35 @@ class CallbacksDescriptor:  public Descriptor {
 };
 
 
+template <class T>
+bool IsPropertyDescriptor(T* desc) {
+  switch (desc->type()) {
+    case NORMAL:
+    case FIELD:
+    case CONSTANT_FUNCTION:
+    case HANDLER:
+    case INTERCEPTOR:
+      return true;
+    case CALLBACKS: {
+      Object* callback_object = desc->GetCallbackObject();
+      // Non-JavaScript (i.e. native) accessors are always a property, otherwise
+      // either the getter or the setter must be an accessor. Put another way:
+      // If we only see map transitions and holes in a pair, this is not a
+      // property.
+      return (!callback_object->IsAccessorPair() ||
+              AccessorPair::cast(callback_object)->ContainsAccessor());
+    }
+    case MAP_TRANSITION:
+    case ELEMENTS_TRANSITION:
+    case CONSTANT_TRANSITION:
+    case NULL_DESCRIPTOR:
+      return false;
+  }
+  UNREACHABLE();  // keep the compiler happy
+  return false;
+}
+
+
 class LookupResult BASE_EMBEDDED {
  public:
   explicit LookupResult(Isolate* isolate)
@@ -261,10 +290,9 @@ class LookupResult BASE_EMBEDDED {
   bool IsFound() { return lookup_type_ != NOT_FOUND; }
   bool IsHandler() { return lookup_type_ == HANDLER_TYPE; }
 
-  // Is the result is a property excluding transitions and the null
-  // descriptor?
+  // Is the result is a property excluding transitions and the null descriptor?
   bool IsProperty() {
-    return IsFound() && IsRealProperty(GetPropertyDetails().type());
+    return IsFound() && IsPropertyDescriptor(this);
   }
 
   bool IsCacheable() { return cacheable_; }