Upgrade V8 to 5.1.281.57  DO NOT MERGE

FPIIM-449

Change-Id: Id981b686b4d587ac31697662eb98bb34be42ad90
(cherry picked from commit 3b9bc31999c9787eb726ecdbfd5796bfdec32a18)
diff --git a/src/global-handles.h b/src/global-handles.h
index 7047d8c..ac8487b 100644
--- a/src/global-handles.h
+++ b/src/global-handles.h
@@ -165,7 +165,7 @@
   // Clear the weakness of a global handle.
   static void* ClearWeakness(Object** location);
 
-  // Clear the weakness of a global handle.
+  // Mark the reference to this object independent of any object group.
   static void MarkIndependent(Object** location);
 
   // Mark the reference to this object externaly unreachable.
@@ -242,6 +242,9 @@
   // can be skipped and false otherwise.
   bool IterateObjectGroups(ObjectVisitor* v, WeakSlotCallbackWithHeap can_skip);
 
+  // Print all objects in object groups
+  void PrintObjectGroups();
+
   // Add an object group.
   // Should be only used in GC callback function before a collection.
   // All groups are destroyed after a garbage collection.