Bring back write barrier modes on the new GC branch.

src/mark-compact.cc

Index: src/mark-compact.cc
===================================================================
--- src/mark-compact.cc	(revision 9191)
+++ src/mark-compact.cc	(working copy)
@@ -2183,7 +2183,7 @@
               heap_,
               map_offset + new_number_of_transitions * step,
               cached_map,
-              SKIP_WRITE_BARRIER);
+              SKIP_WRITE_BARRIER);//Is this OK?

[Vyacheslav Egorov (Chromium), 2011/09/08 11:56:23]

Yes it is we are in the middle of the GC so all incremental activities are
stopped.

         }
       }
 
@@ -2192,6 +2192,8 @@
       for (int i = new_number_of_transitions * step;
            i < number_of_transitions * step;
            i++) {
+        // The undefined object is on a page that is never compacted and never

[Vyacheslav Egorov (Chromium), 2011/09/08 11:56:23]

And it's also root. And we are in the middle of GC

+        // in new space so it is OK to skip the write barrier.
         prototype_transitions->set_unchecked(heap_,
                                              header + i,
                                              undefined,