Made PropertyType handling even more explicit.

src/property-details.h

Index: src/property-details.h
diff --git a/src/property-details.h b/src/property-details.h
index 9df99880846d6df101827163fe738abce670679d..135c2ca01321fb67fbadba602f7f47b6b6fb792e 100644
--- a/src/property-details.h
+++ b/src/property-details.h
@@ -61,12 +61,11 @@ enum PropertyType {
   CALLBACKS                 = 3,
   HANDLER                   = 4,  // only in lookup results, not in descriptors
   INTERCEPTOR               = 5,  // only in lookup results, not in descriptors
+  // All properties before MAP_TRANSITION are real.
   MAP_TRANSITION            = 6,  // only in fast mode
   ELEMENTS_TRANSITION       = 7,
   CONSTANT_TRANSITION       = 8,  // only in fast mode
   NULL_DESCRIPTOR           = 9,  // only in fast mode
-  // All properties before MAP_TRANSITION are real.
-  FIRST_PHANTOM_PROPERTY_TYPE = MAP_TRANSITION,
   // There are no IC stubs for NULL_DESCRIPTORS. Therefore,
   // NULL_DESCRIPTOR can be used as the type flag for IC stubs for
   // nonexistent properties.
@@ -94,6 +93,26 @@ inline bool IsTransitionType(PropertyType type) {
 }
 
 
+inline bool IsRealProperty(PropertyType type) {
+  switch (type) {
+    case NORMAL:
+    case FIELD:
+    case CONSTANT_FUNCTION:
+    case CALLBACKS:
+    case HANDLER:
+    case INTERCEPTOR:
+      return true;
+    case MAP_TRANSITION:
+    case ELEMENTS_TRANSITION:
+    case CONSTANT_TRANSITION:
+    case NULL_DESCRIPTOR:
+      return false;
+  }
+  UNREACHABLE();  // keep the compiler happy
+  return false;
+}
+
+
 // PropertyDetails captures type and attributes for a property.
 // They are used both in property dictionaries and instance descriptors.
 class PropertyDetails BASE_EMBEDDED {
@@ -127,7 +146,7 @@ class PropertyDetails BASE_EMBEDDED {
   }
 
   bool IsProperty() {
-    return type() < FIRST_PHANTOM_PROPERTY_TYPE;
+    return IsRealProperty(type());
   }
 
   PropertyAttributes attributes() { return AttributesField::decode(value_); }