Don't run the second pass of the pending phantom callbacks if the heap has been torn down.

src/global-handles.h

Index: src/global-handles.h
diff --git a/src/global-handles.h b/src/global-handles.h
index 0ee8c20a375adaea6803c11034686b08d806f9d8..1b8994d4765b2fc1cf4e39527411c1c61e4b306f 100644
--- a/src/global-handles.h
+++ b/src/global-handles.h
@@ -304,6 +304,8 @@ class GlobalHandles {
   class NodeIterator;
   class PendingPhantomCallbacksSecondPassTask;
 
+  void ClearPhantomCallbacksTask(PendingPhantomCallbacksSecondPassTask* task);
+
   Isolate* isolate_;
 
   // Field always containing the number of handles to global objects.
@@ -337,6 +339,11 @@ class GlobalHandles {
 
   List<PendingPhantomCallback> pending_phantom_callbacks_;
 
+  // Scheduled task that runs the second pass of the phantom callbacks.
+  // We keep this pointer to send a notification when the heap is being torn
+  // down.
+  PendingPhantomCallbacksSecondPassTask* phantom_callbacks_task_;
+
   friend class Isolate;
 
   DISALLOW_COPY_AND_ASSIGN(GlobalHandles);