Update V8 to r5780 as required by WebKit r71558

Change-Id: Ie3936550b99967a13755930d0dac0a59c3562625
diff --git a/src/global-handles.h b/src/global-handles.h
index 659f86e..37b2b44 100644
--- a/src/global-handles.h
+++ b/src/global-handles.h
@@ -96,7 +96,8 @@
   static bool IsWeak(Object** location);
 
   // Process pending weak handles.
-  static void PostGarbageCollectionProcessing();
+  // Returns true if next major GC is likely to collect more garbage.
+  static bool PostGarbageCollectionProcessing();
 
   // Iterates over all strong handles.
   static void IterateStrongRoots(ObjectVisitor* v);