Reland "Fix memory leak caused by field type in descriptor array."

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index cf6d1613e6545724162d07b7fa22e4ab759f58c6..5961dc060f82ac581ccda19073d2375e2dfe9b34 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -6478,9 +6478,12 @@ class Map: public HeapObject {
 
   Map* FindLastMatchMap(int verbatim, int length, DescriptorArray* descriptors);
 
+  // Update field type of the given descriptor to new representation and new
+  // type. The type must be prepared for storing in descriptor array:
+  // it must be either a simple type or a map wrapped in a weak cell.
   void UpdateFieldType(int descriptor_number, Handle<Name> name,
                        Representation new_representation,
-                       Handle<HeapType> new_type);
+                       Handle<Object> new_wrapped_type);
 
   void PrintReconfiguration(FILE* file, int modify_index, PropertyKind kind,
                             PropertyAttributes attributes);