Update V8 to r5716 as required by WebKit r70949

Change-Id: I0d5cd05bb0427af33e5c9f6efdc209366a32bde3
diff --git a/src/global-handles.h b/src/global-handles.h
index c4c59fd..659f86e 100644
--- a/src/global-handles.h
+++ b/src/global-handles.h
@@ -95,9 +95,8 @@
   // Tells whether global handle is weak.
   static bool IsWeak(Object** location);
 
-  // Process pending weak handles.  Returns true if any weak handle
-  // callback has been invoked.
-  static bool PostGarbageCollectionProcessing();
+  // Process pending weak handles.
+  static void PostGarbageCollectionProcessing();
 
   // Iterates over all strong handles.
   static void IterateStrongRoots(ObjectVisitor* v);