Update V8 to r6387 as required by WebKit r76408

Change-Id: Icfc5385b0996bd592f8b1ac8cbb44767ee09f1f6
diff --git a/src/zone.h b/src/zone.h
index dde722f..e299f15 100644
--- a/src/zone.h
+++ b/src/zone.h
@@ -1,4 +1,4 @@
-// Copyright 2006-2008 the V8 project authors. All rights reserved.
+// Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
@@ -71,6 +71,8 @@
 
   static inline void adjust_segment_bytes_allocated(int delta);
 
+  static unsigned allocation_size_;
+
  private:
 
   // All pointers returned from New() have this alignment.