Fix for an assertion failure in Map::FindTransitionToField(...). Appeared after r25136.

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 85584c43e400f44eabb37ac66f96470efbbb72c2..0288bfb81b7e54558da93d22665009a8c30f7d1e 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -1886,8 +1886,9 @@ Handle<Map> Map::FindTransitionToField(Handle<Map> map, Handle<Name> key) {
   TransitionArray* transitions = map->transitions();
   int transition = transitions->Search(FIELD, *key, NONE);
   if (transition == TransitionArray::kNotFound) return Handle<Map>::null();
-  DCHECK_EQ(FIELD, transitions->GetTargetDetails(transition).type());
-  DCHECK_EQ(NONE, transitions->GetTargetDetails(transition).attributes());
+  PropertyDetails details = transitions->GetTargetDetails(transition);
+  if (details.type() != FIELD) return Handle<Map>::null();
+  DCHECK_EQ(NONE, details.attributes());
   return Handle<Map>(transitions->GetTarget(transition));
 }