Attempt to collect more garbage before panicking with out of memory.

src/global-handles.h

Index: src/global-handles.h
diff --git a/src/global-handles.h b/src/global-handles.h
index 659f86eca70251687a009c585e4d59936e731edd..c4c59fdf4d919330173be5a2effdb8053f7cb6ec 100644
--- a/src/global-handles.h
+++ b/src/global-handles.h
@@ -95,8 +95,9 @@ class GlobalHandles : public AllStatic {
   // Tells whether global handle is weak.
   static bool IsWeak(Object** location);
 
-  // Process pending weak handles.
-  static void PostGarbageCollectionProcessing();
+  // Process pending weak handles.  Returns true if any weak handle
+  // callback has been invoked.
+  static bool PostGarbageCollectionProcessing();
 
   // Iterates over all strong handles.
   static void IterateStrongRoots(ObjectVisitor* v);